Income Taxes (Deferred Taxes) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
deferred tax asset, warrant remeasurement	$ 4,746	$ 0
Deferred tax assets:
Net operating loss carryforward and federal credits	20,596	30,981
Post-retirement employee benefits	27,060	36,589
Employee benefits other than post-retirement	13,785	13,773
Inventory reserve	2,727	2,924
Deferred revenue	7,728	8,650
Other	4,411	2,344
Deferred tax assets	81,053	95,261
Deferred tax liabilities:
Accelerated depreciation	(186,015)	(175,572)
Partnership items	(8,777)	(9,489)
State taxes	(8,564)	(6,830)
Valuation allowance against deferred tax assets	(229)	(229)
Deferred tax liabilities	203,585	192,120
Net deferred tax (liability)	$ (122,532)	$ (96,859)