Summary of Principal Components of Net Deferred Income Tax Liability (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Asset Retirement Obligations	$ 1,073	$ 647
Deferred Tax Assets, Operating Loss Carryforwards	175,221	163,437
Deferred tax assets:
Less: Valuation allowance	(114,939)	(128,650)
Total net deferred tax assets	81,906	44,610
Deferred income taxes	0	1,949
Deferred Tax Liabilities, Property, Plant and Equipment	83,330	33,413
Deferred Tax Liabilities, Derivatives	0	9,248
Deferred Tax Liabilities, Net	83,330	42,661
Deferred Tax Liabilities, Net, Noncurrent	(1,424)	0
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	1,236	2,471
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits	340	441
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	880	546
Deferred Tax Assets, Derivative Instruments	4,191	0
Deferred Tax Asset, Interest Carryforward	11,463	3,128
Deferred Tax Assets, Other	2,441	2,590
Deferred Tax Assets, Gross	$ 196,845	$ 173,260