Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements and Marketable Securities - Summary of Company's Available-for-Sale Securities (Detail)

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Fair Value Measurements and Marketable Securities - Summary of Company's Available-for-Sale Securities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis $ 13,002 $ 39,112
Unrealized Gain 1 1
Unrealized Loss (3) (22)
Fair Value 13,000 39,091
Money Market Funds    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 2,746 5,421
Unrealized Gain 0 0
Unrealized Loss 0 0
Fair Value 2,746 5,421
Corporate Debt Securities    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 4,208 12,578
Unrealized Gain 0 1
Unrealized Loss (2) (8)
Fair Value 4,206 12,571
Government Securities    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 5,299 21,783
Unrealized Gain 1 0
Unrealized Loss (1) (14)
Fair Value 5,299 21,769
Certificates of Deposit    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis   696
Unrealized Gain   0
Unrealized Loss   0
Fair Value   696
Commercial Paper    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 10,966 6,145
Unrealized Gain 0 0
Unrealized Loss 0 0
Fair Value 10,966 6,145
Marketable Securities Including Cash Equivalents    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 23,219 48,531
Unrealized Gain 1 1
Unrealized Loss (3) (22)
Fair Value 23,217 48,510
Less Cash Equivalents    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 10,217 9,419
Unrealized Gain 0 0
Unrealized Loss 0 0
Fair Value $ 10,217 9,419
Municipal Securities    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis   1,908
Unrealized Gain   0
Unrealized Loss   0
Fair Value   $ 1,908