Summary of Principal Components of Net Deferred Income Tax Liability (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Property and equipment	$ 417,535	$ 0
Pension and postretirement benefits	2,276	2,370
Share-based compensation	7,393	7,171
Net operating loss (“NOL”) carryforwards	222,971	102,098
Deferred gains	30,382	33,704
Other	16,637	19,875
Deferred tax assets, gross	697,194	165,218
Less: Valuation allowance	(662,909)	(105,615)
Total net deferred tax assets	34,285	59,603
Deferred tax liabilities:
Fair value of derivative instruments	34,285	57,707
Property and equipment	0	6,347
Deferred tax liabilities, gross	34,285	64,054
Deferred tax liabilities, net	$ 0	$ 4,451