Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets
Accrued employee benefits and compensation	$ 10,591	$ 13,124
Postretirement benefit obligations	23,066	28,923
Tax credit carryforwards	18,574	16,142
Reserves and accruals	6,014	4,097
Depreciation and amortization	19,134	17,276
Other	1,751	2,143
Total deferred tax assets	79,130	81,705
Less deferred tax asset valuation allowance	(466)	(59,442)
Total deferred tax assets, net of valuation allowance	78,664	22,263
Deferred tax liabilities
Investment in joint ventures, net	1,559	2,265
Depreciation and amortization	15,654	16,614
Other	332	380
Total deferred tax liabilities	17,545	19,259
Net deferred tax asset	$ 61,119	$ 3,004