Income Taxes - Deferred tax (liabilities) assets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Temporary differences [Abstract]
Property, plant and equipment	$ (44,448)	$ (46,016)
Goodwill and other intangible assets	(2,684)	1,605
Investments, primarily gains and losses not yet recognized for tax purposes	4,750	3,128
Accrued expenses not deductible until paid	11,865	16,213
Deferred compensation and retiree benefits not deductible until paid	37,041	61,703
Other temporary differences, net	25	244
Total temporary differences	6,549	36,877
Federal and state net operating loss carryforwards	21,123	6,984
Valuation allowance for state deferred tax assets	(1,078)	(556)
Deferred Tax Assets, Net	$ 26,594	$ 43,305