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
Beginning Balance at Dec. 31, 2014	$ 497	$ 576,504	$ 423,956	$ (17,027)	$ (119,749)	$ 864,181
Net income	0	0	37,447	0	0	37,447
Cash dividends	0	0	(18,957)	0	0	(18,957)
Purchases of treasury shares	0	0	0	0	(10,672)	(10,672)
Net issuance of shares to employee benefit plans and other stock plans, including tax benefit	0	(3,568)	0	0	4,060	492
Stock-based compensation	0	2,676	0	0	0	2,676
Other comprehensive income	0	0	0	804	0	804
Ending Balance at Jun. 30, 2015	497	575,612	442,446	(16,223)	(126,361)	875,971
Beginning 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)
Purchases 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
Ending Balance at Jun. 30, 2016	$ 497	$ 573,067	$ 482,074	$ (11,147)	$ (148,138)	$ 896,353