Income Taxes - Deferred Tax Balance Classification in Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Long term deferred tax assets	$ 1,801	$ 2,433
Long term deferred tax liabilities	(518,912)	(668,580)
Net long term deferred taxes	(517,111)	(666,147)
Net deferred tax liabilities	$ (517,111)	$ (666,147)