Fair Value of Financial Instruments - Schedule of Major Categories of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Commercial Paper [Member]
Assets:
Assets	$ 25,506	$ 21,041
Certificates of Deposit [Member]
Assets:
Assets	4,000	6,000
Level 2 [Member] | Commercial Paper [Member]
Assets:
Assets	25,506	21,041
Level 2 [Member] | Certificates of Deposit [Member]
Assets:
Assets	4,000	6,000
Interest Rate Swap [Member]
Assets:
Assets		17
Liabilities:
Liabilities	523
Interest Rate Swap [Member] | Level 2 [Member]
Assets:
Assets		$ 17
Liabilities:
Liabilities	$ 523