Income Taxes - Differences in Provision for Income Taxes from Amount Computed by Applying Statutory U.S. Federal Income Tax Rate to Income (Loss) from Operations Before Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S. statutory rate		$ 13,873	$ 9,903	$ (4,122)
Permanent items		(1,916)	(570)	(782)
Write-off of foreign tax and research credits		0	7,125	0
Foreign tax credits		0	(319)	306
Uncertain tax positions		3,128	1,529	2,523
Other tax credits		(175)	90	(120)
State and local taxes		1,252	433	478
Impact of rate change on deferred taxes	$ 45,100	45,129	(383)	749
True-up of prior year tax		7	(2,751)	1,191
Foreign tax rate differential		97	(242)	46
Valuation allowance	$ (141,100)	(141,094)
Valuation allowance			(13,292)	2,704
Benefit of windfall related to stock compensation		(2,723)	0	0
Increase in indemnification deferred tax asset		(1,055)	0	0
Other		(269)	9	(5)
Income tax (benefit) provision		$ (83,746)	$ 1,532	$ 2,968