Income Taxes - Schedule of Deferred Tax Asset and Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Assets
Net operating losses	$ 56,769	$ 207,633
Alternative minimum tax credits	114,149	208,624
Foreign tax credits	3,473	3,541
Other business credits	3,380	3,524
Derivative instruments	0	6,645
Incentive compensation	17,378	15,898
Deferred compensation	5,690	6,065
Post-retirement benefits	6,799	7,265
Equity method investments	20,746	21,812
Capital loss carryforward	8,877	0
Other	2,957	492
Less: valuation allowance	(14,943)	(16,711)
Total	225,275	464,788
Deferred Tax Liabilities
Properties and equipment	670,704	691,818
Derivative instruments	13,168	0
Total	683,872	691,818
Net deferred tax liabilities	$ 458,597	$ 227,030