Income Taxes - Balance Sheet Classification of Net Deferred Income Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current assets	$ 0	$ 37,504
Noncurrent assets	10,731
Noncurrent assets		21,737
Noncurrent liabilities	(60,018)
Noncurrent liabilities		(126,009)
Net deferred income tax asset (liability)	$ (49,287)	$ (66,768)