Income Taxes - Summary of Source and Tax Effects of Temporary Differences between Financial Reporting and Tax Bases of Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred income taxes:
Total deferred income tax assets	$ (643,227)	$ (549,969)
Total deferred income tax liabilities	2,129,041	2,373,350
Total net deferred income tax liabilities	1,485,814	1,823,381
Total deferred income tax liabilities (assets):
Drilling and development costs expensed for income tax reporting	1,100,061	1,469,320
Tax depreciation in excess of book depreciation	974,520	904,030
Investment in Equitrans Midstream	(109,883)	(10,359)
Incentive compensation and deferred compensation plans	(16,923)	(24,682)
Net operating loss carryforwards	(635,446)	(429,983)
Alternative minimum tax credit carryforward	(190,992)	(308,727)
Federal tax credits	(59,854)	(37,710)
Unrealized gains (losses)	54,460	(28,096)
Interest disallowance limitation	(46,776)	(35,358)
Other	(6,797)	(26,462)
Total excluding valuation allowances	1,062,370	1,471,973
Valuation allowances	$ 423,444	$ 351,408