Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income	$ 89,910	$ 70,581	$ 42,594
Other comprehensive income (loss), net of tax:
Net gain (loss) arising during the period, net of tax expense (benefit) of $(15,598), $21,424 and $(5,968)	(24,396)	33,510	(9,334)
Prior service credit arising during the period, net of tax expense of $0, $0 and $2,159	0	0	3,273
Amortization of actuarial loss included in net periodic cost, net of tax expense of $6,488, $9,024 and $7,208	10,149	14,114	11,275
Amortization of prior service credit included in net periodic cost, net of tax benefit of $(3,468), $(3,482) and $(3,343)	(5,425)	(5,446)	(5,230)
Other comprehensive income (loss), net of tax	(19,672)	42,178	(16)
Comprehensive income	$ 70,238	$ 112,759	$ 42,578