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Fair Value Measurements and Marketable Securities - Financial Assets at Fair Value on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
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Mar. 31, 2013
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Dec. 31, 2012
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total cash equivalents and marketable securities |
$ 104,102
|
$ 70,825
|
|
Basis of Fair Value Measurements, Level 1 [Member]
|
|
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| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total cash equivalents and marketable securities |
9,345
|
5,886
|
|
Basis of Fair Value Measurements, Level 2 [Member]
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total cash equivalents and marketable securities |
94,757
|
64,939
|
|
Basis of Fair Value Measurements, Level 3 [Member]
|
|
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| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
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|
|
Money market funds [Member]
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|
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| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
9,345
|
5,886
|
|
Money market funds [Member] | Basis of Fair Value Measurements, Level 1 [Member]
|
|
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| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
9,345
|
5,886
|
|
Money market funds [Member] | Basis of Fair Value Measurements, Level 2 [Member]
|
|
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| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total cash equivalents and marketable securities |
|
|
|
Money market funds [Member] | Basis of Fair Value Measurements, Level 3 [Member]
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|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
|
|
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Certificates of deposit [Member]
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| Schedule of Available-for-sale Securities [Line Items] |
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| Total cash equivalents and marketable securities |
2,125
|
1,185
|
|
Certificates of deposit [Member] | Basis of Fair Value Measurements, Level 1 [Member]
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| Schedule of Available-for-sale Securities [Line Items] |
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| Total cash equivalents and marketable securities |
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|
|
Certificates of deposit [Member] | Basis of Fair Value Measurements, Level 2 [Member]
|
|
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| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
2,125
|
1,185
|
|
Certificates of deposit [Member] | Basis of Fair Value Measurements, Level 3 [Member]
|
|
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| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
|
|
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Corporate debt securities [Member]
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
42,978
|
20,242
|
|
Corporate debt securities [Member] | Basis of Fair Value Measurements, Level 1 [Member]
|
|
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| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total cash equivalents and marketable securities |
|
|
|
Corporate debt securities [Member] | Basis of Fair Value Measurements, Level 2 [Member]
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total cash equivalents and marketable securities |
42,978
|
20,242
|
|
Corporate debt securities [Member] | Basis of Fair Value Measurements, Level 3 [Member]
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total cash equivalents and marketable securities |
|
|
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Government securities [Member]
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| Schedule of Available-for-sale Securities [Line Items] |
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| Total cash equivalents and marketable securities |
35,664
|
27,899
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Government securities [Member] | Basis of Fair Value Measurements, Level 1 [Member]
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| Schedule of Available-for-sale Securities [Line Items] |
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| Total cash equivalents and marketable securities |
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Government securities [Member] | Basis of Fair Value Measurements, Level 2 [Member]
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| Schedule of Available-for-sale Securities [Line Items] |
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| Total cash equivalents and marketable securities |
35,664
|
27,899
|
|
Government securities [Member] | Basis of Fair Value Measurements, Level 3 [Member]
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| Schedule of Available-for-sale Securities [Line Items] |
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| Total cash equivalents and marketable securities |
|
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Commercial paper [Member]
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|
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| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
13,990
|
15,613
|
|
Commercial paper [Member] | Basis of Fair Value Measurements, Level 1 [Member]
|
|
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| Schedule of Available-for-sale Securities [Line Items] |
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| Total cash equivalents and marketable securities |
|
|
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Commercial paper [Member] | Basis of Fair Value Measurements, Level 2 [Member]
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|
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| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
13,990
|
15,613
|
|
Commercial paper [Member] | Basis of Fair Value Measurements, Level 3 [Member]
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|
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| Schedule of Available-for-sale Securities [Line Items] |
|
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| Total cash equivalents and marketable securities |
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