Summary of Principal Components of Net Deferred Income Tax Liability (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Property and equipment	$ 183,303	$ 417,535
Pension and postretirement benefits	710	2,276
Share-based compensation	28	7,393
Net operating loss (“NOL”) carryforwards	87,622	222,971
Deferred Tax Assets, Derivative Instruments	9,579
Deferred gains	0	30,382
Other	7,166	16,637
Deferred tax assets, gross	288,408	697,194
Less: Valuation allowance	(288,408)	(662,909)
Total net deferred tax assets	0	34,285
Deferred tax liabilities:
Fair value of derivative instruments	0	34,285
Deferred tax liabilities, gross	0	34,285
Deferred tax liabilities, net	$ 0	$ 0