Income Taxes - Schedule of Composition of Net Deferred Tax Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets
Net operating losses	$ 22,177	$ 22,360
Alternative minimum tax credits	0	22,120
Incentive compensation	16,427	17,776
Deferred compensation	5,753	5,463
Post-retirement benefits	7,482	7,847
Equity method investments	0	21,454
Leases	7,709	8,192
Capital loss carryforward	16,486	0
Other	3,267	1,336
Less: valuation allowance	(28,231)	(31,763)
Total	51,070	74,785
Deferred Tax Liabilities
Properties and equipment	809,919	768,692
Equity method investments	1,649	0
Leases	7,709	8,192
Derivative instruments	5,988	5
Total	825,265	776,889
Net deferred tax liabilities	$ 774,195	$ 702,104