Fair Value Measurements - Narrative (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	May 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, current	$ 32,905	$ 37,955
Amended Credit Facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit facility repayment feature	7,100	$ 2,000	$ 500
Cash and cash equivalent threshold	$ 50,000		$ 50,000