CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 20,224	$ 30,211	$ 12,014
Other comprehensive income (loss), net of tax:
Total other comprehensive income (loss), net	5,051	(84,786)	35,223
Comprehensive income (loss)	25,275	(54,575)	47,237
Defined benefit pension plans [Member]
Other comprehensive income (loss), net of tax:
Defined benefit pension plans	12,821	(75,807)	41,656
OPEB [Member]
Other comprehensive income (loss), net of tax:
Defined benefit pension plans	$ (7,770)	$ (8,979)	$ (6,433)