Income Tax - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Operating expenses not currently deductible	$ 11,232	$ 18,721
Stock option and other employee benefit plans	15,932	19,665
Total deferred income tax assets	27,164	38,386
Intangible assets	(60,189)	(103,754)
Property and equipment	(5,699)	(3,207)
Other	(190)	(204)
Total deferred income tax liabilities	(66,078)	(107,165)
Net deferred income tax liabilities	$ (38,914)	$ (68,779)