CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning balance (shares) at Dec. 31, 2015		24,732
Beginning balance at Dec. 31, 2015	$ 245,225	$ 247	$ 76,746	$ 288,358	$ (34,585)	$ (85,541)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,187			37,187
Other comprehensive income (loss), net of tax	(13,365)				(13,365)
Stock repurchased	(1,155)					(1,155)
Stock issued under employee plans (shares)		119
Stock issued under employee plans	1,158	$ 2	1,156
Stock-based compensation expense	4,009		4,009
Stock issued to directors (shares)		7
Stock issued to directors	350		350
Recently adopted accounting standards	47		126	(79)
Ending balance (shares) at Dec. 31, 2016		24,858
Ending balance at Dec. 31, 2016	273,456	$ 249	82,387	325,466	(47,950)	(86,696)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	49,317			49,317
Other comprehensive income (loss), net of tax	27,802				27,802
Stock repurchased	(2,799)					(2,799)
Stock issued under employee plans (shares)		152
Stock issued under employee plans	1,351	$ 1	1,350
Stock-based compensation expense	3,868		3,868
Stock issued to directors (shares)		8
Stock issued to directors	$ 401		401
Ending balance (shares) at Dec. 31, 2017	25,018	25,018
Ending balance at Dec. 31, 2017	$ 353,396	$ 250	88,006	374,783	(20,148)	(89,495)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	34,944			34,944
Other comprehensive income (loss), net of tax	(22,537)				(22,537)
Stock repurchased	(974)					(974)
Stock issued under employee plans (shares)		225
Stock issued under employee plans	855	$ 3	852
Stock-based compensation expense	1,619		1,619
Stock issued to directors (shares)		11
Stock issued to directors	$ 374		374
Ending balance (shares) at Dec. 31, 2018	25,254	25,254
Ending balance at Dec. 31, 2018	$ 369,275	$ 253	$ 90,851	$ 411,325	$ (42,685)	$ (90,469)