Deferred Income Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Loss and credit carryforwards	$ 11,184	$ 6,714
Accrued expenses	2,089	2,096
Stock-based compensation	9,914	9,823
Total deferred tax assets	23,187	18,633
Valuation allowance	(4,803)	(1,610)
Net deferred tax assets	18,384	17,023
Deferred tax liabilities:
Fixed assets	(5,909)	(5,738)
Intangible assets	(86,462)	(117,172)
Prepaid expenses	(305)	(2,135)
Total deferred tax liabilities	(92,676)	(125,045)
Net deferred tax liability	$ (74,292)	$ (108,022)