Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets
Accrued employee benefits and compensation	$ 8,927	$ 10,591
Postretirement benefit obligations	2,736	23,066
Tax credit carryforwards	9,825	18,574
Reserves and accruals	6,671	6,014
Depreciation and amortization	20,717	19,134
Other	3,715	1,751
Total deferred tax assets	52,591	79,130
Less deferred tax asset valuation allowance	(466)	(466)
Total deferred tax assets, net of valuation allowance	52,125	78,664
Deferred tax liabilities
Investment in joint ventures, net	0	1,559
Depreciation and amortization	15,839	15,654
Other	238	332
Total deferred tax liabilities	16,077	17,545
Net deferred tax asset	$ 36,048	$ 61,119