Income Taxes (Deferred Taxes) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
deferred tax asset, warrant remeasurement	$ 7,314	$ 3,974
Deferred tax assets:
Net operating loss carryforward and federal credits	55,760	17,021
Post-retirement employee benefits	13,777	8,716
Employee benefits other than post-retirement	8,751	9,229
Inventory reserve	2,374	1,739
Deferred revenue	4,389	3,016
Other	4,713	4,317
Deferred tax assets	97,078	48,012
Deferred tax liabilities:
Accelerated depreciation	(189,719)	(129,201)
Partnership items	(5,850)	(5,858)
State taxes	(14,474)	(12,119)
Valuation allowance against deferred tax assets	(278)	(278)
Deferred tax liabilities	210,321	147,456
Net deferred tax (liability)	$ (113,243)	$ (99,444)