Consolidated Condensed Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net earnings	$ 5,483	$ 8,327	$ 7,901	$ 4,227	$ 6,001	$ 10,231	$ 8,814	$ 4,632	$ 25,938	$ 29,678	$ 24,617
Other comprehensive income :
Foreign currency translation adjustment									(847)	(1,721)	172
Employee benefit funded status adjustment, net of tax									(77)	(2,611)	6,252
Comprehensive income									$ 25,014	$ 25,346	$ 31,041