Fair Value Measurements - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Assets
Cash Equivalents		$ 40,187	$ 39,982
Total assets		40,187	39,982
Not Subject to Leveling [Member]
Assets
Cash Equivalents	[1]	40,187	39,982
Total assets	[1]	$ 40,187	$ 39,982

[1] Certain cash equivalents that are valued using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy.