Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net income	$ 7,321	$ 9,719	$ 14,586	$ 17,682
Other comprehensive income (loss), net of tax:
Total other comprehensive income, net	1,587	587	3,172	1,174
Comprehensive income	8,908	10,306	17,758	18,856
Defined Benefit Pension Plans [Member]
Other comprehensive income (loss), net of tax:
Amortization of prior service cost/credit	186	186	372	372
Amortization of net actuarial losses	2,683	1,552	5,365	3,103
Other Postretirement Benefit Plans [Member]
Other comprehensive income (loss), net of tax:
Amortization of prior service cost/credit	(2,441)	(2,442)	(4,883)	(4,883)
Amortization of net actuarial losses	1,159	1,291	2,318	2,582
Total other comprehensive income, net			$ (2,565)