Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 42,594	$ 40,266	$ 40,394
Other comprehensive income (loss), net of tax:
Net gain (loss) arising during the period, net of tax of $(5,968), $(21,960) and $5,132	(9,334)	(34,347)	8,027
Prior service (cost) credit arising during the period, net of tax of $2,159, $2,264 and $(279)	3,273	3,541	(436)
Amortization of actuarial loss included in net periodic cost, net of tax of $7,208, $5,414 and $4,994	11,275	8,469	7,811
Amortization of prior service credit included in net periodic cost, net of tax of $(3,343), $(3,062) and $(3,001)	(5,230)	(4,790)	(4,695)
Recognition of deferred taxes related to actuarial gain on OPEB obligations	0	0	3,015
Other comprehensive income (loss), net of tax	(16)	(27,127)	13,722
Comprehensive income	$ 42,578	$ 13,139	$ 54,116