Fair Value Measurements - Schedule of Fair Value of Financial Assets Measured on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial Assets
Total financial assets	$ 90,538	$ 105,524
Money Market Funds [Member]
Financial Assets
Total financial assets	90,238	105,224
Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	300	300
Level 1 [Member]
Financial Assets
Total financial assets	90,538	105,524
Level 1 [Member] | Money Market Funds [Member]
Financial Assets
Total financial assets	90,238	105,224
Level 1 [Member] | Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	$ 300	$ 300