Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$ 70,581	$ 42,594	$ 40,266
Other comprehensive income (loss), net of tax:
Net gain (loss) arising during the period, net of tax expense (benefit) of $21,424, $(5,968) and $(21,960)	33,510	(9,334)	(34,347)
Prior service credit arising during the period, net of tax expense of $0, $2,159 and $2,264	0	3,273	3,541
Amortization of actuarial loss included in net periodic cost, net of tax expense of $9,024, $7,208 and $5,414	14,114	11,275	8,469
Amortization of prior service credit included in net periodic cost, net of tax benefit of $(3,482), $(3,343) and $(3,062)	(5,446)	(5,230)	(4,790)
Other comprehensive income (loss), net of tax	42,178	(16)	(27,127)
Comprehensive income	$ 112,759	$ 42,578	$ 13,139