Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements	$ 0	$ 2,116	$ 0
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(7,770)	3,795	15,315
Net earnings	97,339	49,554	55,983
Defined benefit pension and other postretirement employee benefits:
Net gain arising during the period, net of tax of $2,409, $248 and $5,814	6,745	379	8,944
Amortization of actuarial loss included in net periodic cost, net of tax of $1,305, $1,576, and $4,972	1,951	2,321	7,647
Amortization of prior service credit included in net periodic cost, net of tax of $(601), $(669), and $(829)	926	1,021	1,276
Other comprehensive (loss) income, net of tax	7,770	3,795	15,315
Comprehensive income	$ 105,109	$ 53,349	$ 71,298