Fair Value of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets:
Restricted cash	$ 20	$ 20
Liabilities:
Contingent consideration	47,400	48,400
Unobservable Inputs (Level 3)
Liabilities:
Contingent consideration	47,400	48,400
Recurring
Assets:
Cash and cash equivalents	42,437	50,422
Restricted cash	20	20
Total assets	42,457	50,442
Liabilities:
Contingent consideration	47,400	48,400
Total liabilities	47,400	48,400
Recurring | Active Markets (Level 1)
Assets:
Cash and cash equivalents	42,437	50,422
Restricted cash	20	20
Total assets	42,457	50,442
Liabilities:
Contingent consideration	0	0
Total liabilities	0	0
Recurring | Observable Inputs (Level 2)
Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Total assets	0	0
Liabilities:
Contingent consideration	0	0
Total liabilities	0	0
Recurring | Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Total assets	0	0
Liabilities:
Contingent consideration	47,400	48,400
Total liabilities	$ 47,400	$ 48,400