Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in-Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income [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	38,800	0	0	38,800
Cash dividends	0	0	(18,958)	0	0	(18,958)
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	(5,945)	0	0	4,088	(1,857)
Stock-based compensation	0	2,286	0	0	0	2,286
Other comprehensive income	0	0	0	11,271	0	11,271
Balance at Jun. 30, 2016	497	573,067	482,074	(11,147)	(148,138)	896,353
Balance at Dec. 31, 2016	497	575,078	501,761	(21,520)	(142,500)	913,316
Net income	0	0	41,638	0	0	41,638
Cash dividends	0	0	(20,044)	0	0	(20,044)
Net issuance of shares to employee benefit plans and other stock plans, including tax benefit	0	(4,702)	0	0	3,886	(816)
Stock-based compensation	0	2,733	(95)	0	0	2,638
Other comprehensive income	0	0	0	3,629	0	3,629
Balance at Jun. 30, 2017	$ 497	$ 573,109	$ 523,260	$ (17,891)	$ (138,614)	$ 940,361