Income Taxes - Deferred Tax Assets Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Employee and retiree benefit plans	$ 31,804	$ 42,950
Capital loss carryforwards	12,853	18,668
Depreciation and amortization	(176,592)	(238,321)
Inventories	8,548	11,519
Allowances and accruals	4,572	9,338
Interest rate exchange agreement	5,007	10,442
Other	(8,019)	(90)
Total gross deferred tax (liabilities)	(121,827)	(145,494)
Capital loss valuation allowance	(12,853)	(18,668)
Total deferred tax (liabilities), net of valuation allowances	$ (134,680)	$ (164,162)