Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in-Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Common Stock in Treasury [Member]	Total
Balance at Dec. 31, 2015	$ 497	$ 576,726	$ 462,232	$ (22,418)	$ (135,033)	$ 882,004
Net income	0	0	18,891	0	0	18,891
Cash dividends	0	0	(9,473)	0	0	(9,473)
Purchase of treasury shares	0	0	0	0	(17,193)	(17,193)
Net issuance of shares to employee benefit plans and other stock plans, including tax benefit	0	(4,584)	0	0	1,923	(2,661)
Stock-based compensation	0	1,612	0	0	0	1,612
Other comprehensive income	0	0	0	8,547	0	8,547
Balance at Mar. 31, 2016	497	573,754	471,650	(13,871)	(150,303)	881,727
Balance at Dec. 31, 2016	497	575,078	501,761	(21,520)	(142,500)	913,316
Net income	0	0	20,279	0	0	20,279
Cash dividends	0	0	(10,020)	0	0	(10,020)
Net issuance of shares to employee benefit plans and other stock plans, including tax benefit	0	(3,712)	0	0	2,882	(830)
Stock-based compensation	0	2,261	(95)	0	0	2,166
Other comprehensive income	0	0	0	1,928	0	1,928
Balance at Mar. 31, 2017	$ 497	$ 573,627	$ 511,925	$ (19,592)	$ (139,618)	$ 926,839