Income Taxes (Deferred Taxes) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
deferred tax asset, warrant remeasurement	$ 33,940	$ 17,174
Deferred tax assets:
Net operating loss carryforward and federal credits	71,762	40,467
Post-retirement employee benefits	7,140	6,355
Employee benefits other than post-retirement	8,545	9,435
Inventory reserve	2,288	2,055
Deferred revenue	12,608	5,132
Other	9,366	9,309
Deferred tax assets	160,121	98,997
Deferred Tax Assets, Capital and Operating Leases	14,472	9,070
Deferred tax liabilities:
Accelerated depreciation	(257,765)	(192,651)
Partnership items	(6,044)	(6,088)
State taxes	(11,143)	(12,355)
Valuation allowance against deferred tax assets	(2,293)	(1,412)
Deferred tax liabilities	301,386	226,473
Net deferred tax (liability)	(141,265)	(127,476)
Deferred Tax Liabilities, Leasing Arrangements	(14,264)	(9,051)
Deferred Tax Liabilities, Goodwill	$ (9,877)	$ (4,916)