Summary of Significant Accounting Policies - Recently Issued Accounting Standards (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Adjustment to retained earnings	$ 473,921	$ 424,239
Cost of goods sold	12,080	$ 12,606
Pro forma | Difference between revenue guidance before and after 606 | ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Adjustment to retained earnings	500
Acceleration of revenue	1,500
Cost of goods sold	500
Reserve for returns	$ 1,500