Income Taxes - Schedule of Deferred Tax Asset and Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets
Net operating losses	$ 207,633	$ 352,001
Alternative minimum tax credits	208,624	218,773
Foreign tax credits	3,541	3,816
Other business credits	3,524	0
Derivative instruments	6,645	13,771
Incentive compensation	15,898	22,852
Deferred compensation	6,065	8,217
Post-retirement benefits	7,265	13,865
Equity method investments	21,812	0
Other	492	2,743
Less: valuation allowance	(16,711)	(5,186)
Total	464,788	630,852
Deferred Tax Liabilities
Properties and equipment	691,818	1,207,545
Equity method investments	0	2,754
Total	691,818	1,210,299
Net deferred tax liabilities	$ 227,030	$ 579,447