Income Taxes - Income Tax Reconciliation Computed at Federal Statutory Rates to Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Benefit from income taxes at statutory rate	$ (770)	$ (411)
State and local income taxes, net of federal tax benefit	(78)	(20)
Stock based compensation	(22)	(20)
Foreign rate differential	(1,237)	45
Research credits	18	59
Permanent non-deductible acquisition-related expense	(301)	(245)
Net (windfall) shortfall on stock based compensation	(117)	471
Other, net	42	20
Reported income tax benefit	$ (2,465)	$ (101)
Benefit from income taxes at statutory rate, tax rate	21.00%	35.00%
State and local income taxes, net of federal tax benefit, tax rate	2.10%	1.70%
Stock based compensation, tax rate	0.60%	1.70%
Foreign rate differential, tax rate	33.80%	(3.80%)
Research credits, tax rate	(0.50%)	(5.00%)
Permanent non-deductible acquisition-related expense, tax rate	8.20%	20.90%
Net (windfall) shortfall on stock based compensation, tax rate	3.20%	(40.10%)
Other, net, tax rate	(1.10%)	(1.80%)
Reported income tax benefit, tax rate	67.30%	8.60%