Quarterly report pursuant to Section 13 or 15(d)

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

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Marketable Securities and Fair Value Measurements - Summary of Company's Available-for-Sale Securities (Detail) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis $ 0 $ 0
Unrealized Gain 0 0
Unrealized Loss 0 0
Fair Value 0 0
Money Market Funds    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 76,373 51,751
Unrealized Gain 0 0
Unrealized Loss 0 0
Fair Value 76,373 51,751
Less Cash Equivalents    
Schedule Of Available For Sale Securities [Line Items]    
Cost Basis 76,373 51,751
Unrealized Gain 0 0
Unrealized Loss 0 0
Fair Value $ 76,373 $ 51,751