Benefit from Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
United States—Federal	$ 1,769	$ 1,033	$ 1,053
United States—State	196	138	113
Total current	1,965	1,171	1,166
Deferred:
United States—Federal	5,760	(4,001)	(3,343)
United States—State	(487)	(334)	(605)
Ireland and United Kingdom	(16,306)	(143)	(9,023)
Change in valuation allowance	22,115	13,276	8,719
Total deferred	11,082	8,798	(4,252)
Provision for (benefit from) income taxes	$ 13,047	$ 9,969	$ (3,086)