Income Taxes - Tax Provisions before Discrete Items Reconciled to Recorded Benefits for Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Provision for income taxes before discrete items	$ 1,900	$ 3,300	$ 4,500	$ 6,100
Interest related to unrecognized tax benefits			100	300
Reassessment of taxes upon filing tax returns	300	(200)	400	(200)
Provision (benefit) related to stock based compensation, including ESPP dispositions	400	(1,400)	(1,900)	(1,700)
Benefit from reassessment of taxes upon foreign statutory tax rate change			(500)
Benefit from reversals of uncertain tax positions due to statute of limitation expirations	(1,800)	(13,500)	(1,800)	(13,500)
Benefit from income taxes	$ 791	$ (11,847)	$ 795	$ (9,041)