Summary of Principal Components of Net Deferred Income Tax Liability (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred tax liabilities:
Property and equipment	$ 248,164	$ 311,002
Fair value of derivative instruments	0	5,268
Total deferred tax liabilities	248,164	316,270
Deferred Tax Assets, Derivative Instruments	1,665	0
Deferred tax assets:
Pension and postretirement benefits	2,248	2,864
Share-based compensation	6,907	10,760
Net operating loss (“NOL”) carryforwards	115,355	102,407
Other	18,029	15,788
Deferred Tax Assets, Gross, Total	144,204	131,819
Less: Valuation allowance	(35,727)	(26,686)
Total deferred tax assets	108,477	105,133
Net deferred tax liability	$ 139,687	$ 211,137