Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 23,840	$ 35,229	$ 18,646
Other Comprehensive Income (Loss), net of tax
Net unrealized gains (losses) on available-for-sale securities	2,163	(1,528)	(7,032)
Defined benefit plan adjustments	731	(1,122)	1,862
Foreign currency translation	5,999	(569)	(3,724)
Other Comprehensive Income (Loss), net of tax	8,893	(3,219)	(8,894)
Comprehensive Income, net of tax	$ 32,733	$ 32,010	$ 9,752