Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Deferred tax assets, Net operating loss carryforwards	$ 604,423	$ 478,975
Deferred tax assets, Canadian net operating loss carryforwards	19,341	18,936
Deferred tax assets, Alternative minimum tax carryforwards	7,781	16,663
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	12,962	32,924
Deferred Tax Assets Non-cash Losses On Derivatives	0	21,064
Deferred Tax Assets, Other	21,885	11,466
Total deferred tax assets	666,392	580,028
Deferred Tax Assets, Valuation Allowance	(19,341)	(18,936)
Deferred Tax Assets, Net	647,051	561,092
Deferred tax liabilities, Property and equipment	(1,903,451)	(2,448,450)
Deferred Tax Liabilities, Other	(3,158)	(2,947)
Total deferred tax liabilities	(1,906,609)	(2,451,397)
Net deferred tax liabilities	$ (1,259,558)	$ (1,890,305)