Fair Value Measurements - Schedule of Fair Value Financial Assets Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financial Assets
Total financial assets	$ 107,234	$ 107,243
Money Market Funds [Member]
Financial Assets
Total financial assets	107,046	107,043
Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	188	200
Level 1 [Member]
Financial Assets
Total financial assets	107,234	107,243
Level 1 [Member] | Money Market Funds [Member]
Financial Assets
Total financial assets	107,046	107,043
Level 1 [Member] | Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	$ 188	$ 200