CONDENSED 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
Balance at beginning of period (shares) at Dec. 31, 2017		25,018
Balance at beginning of period at Dec. 31, 2017	$ 353,396	$ 250	$ 88,006	$ 374,783	$ (20,148)	$ (89,495)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	27,760			27,760
Other comprehensive income (loss), net of tax	(8,578)				(8,578)
Stock repurchased	(956)					(956)
Stock issued (canceled) under employee plans (shares)		83
Stock issued (canceled) under employee plans	848	$ 1	847
Stock-based compensation expense	2,847		2,847
Stock issued to directors (shares)		3
Stock issued to directors	134		134
Balance at end of period (shares) at Sep. 30, 2018		25,104
Balance at end of period at Sep. 30, 2018	377,049	$ 251	91,834	404,141	(28,726)	(90,451)
Balance at beginning of period (shares) at Jun. 30, 2018		25,070
Balance at beginning of period at Jun. 30, 2018	370,715	$ 251	91,177	397,885	(28,280)	(90,318)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	6,256			6,256
Other comprehensive income (loss), net of tax	(446)				(446)
Stock repurchased	(133)					(133)
Stock issued (canceled) under employee plans (shares)		31
Stock issued (canceled) under employee plans	181		181
Stock-based compensation expense	476		476
Stock issued to directors (shares)		3
Stock issued to directors	0
Balance at end of period (shares) at Sep. 30, 2018		25,104
Balance at end of period at Sep. 30, 2018	377,049	$ 251	91,834	404,141	(28,726)	(90,451)
Balance at beginning of period (shares) at Dec. 31, 2018		25,254
Balance at beginning of period at Dec. 31, 2018	369,275	$ 253	90,851	411,325	(42,685)	(90,469)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(52)			(52)
Other comprehensive income (loss), net of tax	10,825				10,825
Stock repurchased	(62)					(62)
Stock issued (canceled) under employee plans (shares)		(43)
Stock issued (canceled) under employee plans	5	$ (1)	6
Stock-based compensation expense	1,611		1,611
Stock issued to directors (shares)		12
Stock issued to directors	252		252
Balance at end of period (shares) at Sep. 30, 2019		25,223
Balance at end of period at Sep. 30, 2019	381,671	$ 252	92,720	411,090	(31,860)	(90,531)
Balance at beginning of period (shares) at Jun. 30, 2019		25,235
Balance at beginning of period at Jun. 30, 2019	387,105	$ 253	92,297	408,086	(23,007)	(90,524)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	3,004			3,004
Other comprehensive income (loss), net of tax	(8,853)				(8,853)
Stock repurchased	(7)					(7)
Stock issued (canceled) under employee plans (shares)		(12)
Stock issued (canceled) under employee plans	5	$ (1)	6
Stock-based compensation expense	417		417
Balance at end of period (shares) at Sep. 30, 2019		25,223
Balance at end of period at Sep. 30, 2019	$ 381,671	$ 252	$ 92,720	$ 411,090	$ (31,860)	$ (90,531)