Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net income	$ 4,981	$ 6,916	$ 19,567	$ 24,598
Other comprehensive income (loss), net of tax:
Total other comprehensive income, net	2,009	620	5,181	1,794
Comprehensive income	6,990	7,536	24,748	26,392
Defined Benefit Pension Plans [Member]
Other comprehensive income (loss), net of tax:
Amortization of prior service cost/credit	186	186	558	558
Amortization of net actuarial losses	3,001	1,584	8,366	4,687
Other Postretirement Benefit Plans [Member]
Other comprehensive income (loss), net of tax:
Amortization of prior service cost/credit	(2,440)	(2,440)	(7,323)	(7,323)
Amortization of net actuarial losses	1,262	1,290	3,580	3,872
Total other comprehensive income, net			$ (3,743)