CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - 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 at Dec. 31, 2016					$ (47,950)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 35,469
Balance at end of period at Sep. 30, 2017					(23,490)
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	27,760			27,760
Other comprehensive income, net of tax	(8,578)				(8,578)
Stock repurchased	(956)					(956)
Stock issued under employee plans (shares)		83
Stock issued 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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASC 606	$ 1,598			$ 1,598