Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net income	$ 31,714	$ 89,910	$ 70,581
Other comprehensive income (loss), net of tax:
Net gain (loss) arising during the period, net of tax expense (benefit) of $(1,913), $(15,598) and $21,424	(2,990)	(24,396)	33,510
Amortization of actuarial loss included in net periodic cost, net of tax expense of $7,794, $6,488 and $9,024	12,190	10,149	14,114
Amortization of prior service credit included in net periodic cost, net of tax benefit of $(3,396), $(3,468) and $(3,482)	(5,311)	(5,425)	(5,446)
Other comprehensive income (loss), net of tax	3,889	(19,672)	42,178
Comprehensive income	$ 35,603	$ 70,238	$ 112,759