Consolidated Statements of Changes in Stockholders' Equity (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, 2011	$ 380	$ 317,329	$ 329,981	$ (6,104)	$ (103,476)	$ 538,110
Net income	0	0	54,558	0	0	54,558
Cash dividends	0	0	(26,712)	0	0	(26,712)
Purchases of treasury shares	0	0	0	0	(15,490)	(15,490)
Net issuance of shares for acquisition	13	25,811	0	0	0	25,824
Net issuance of shares to employee stock plans, including tax benefit	0	(812)	(269)	0	2,476	1,395
Stock-based compensation	0	4,364	0	0	0	4,364
Other comprehensive income	0	0	0	224	0	224
Ending Balance at Dec. 31, 2012	393	346,692	357,558	(5,880)	(116,490)	582,273
Net income	0	0	61,747	0	0	61,747
Cash dividends	0	0	(33,518)	0	0	(33,518)
Purchases of treasury shares	0	0	0	0	(12,459)	(12,459)
Net issuance of shares for acquisition	104	225,447	0	0	(5,779)	219,772
Net issuance of shares to employee stock plans, including tax benefit	0	(2,292)	0	0	7,626	5,334
Stock-based compensation	0	4,305	0	0	0	4,305
Other comprehensive income	0	0	0	(10,885)	0	(10,885)
Ending Balance at Dec. 31, 2013	497	574,152	385,787	(16,765)	(127,102)	816,569
Net income	0	0	75,074	0	0	75,074
Cash dividends	0	0	(36,905)	0	0	(36,905)
Purchases of treasury shares	0	0	0	0	(72)	(72)
Net issuance of shares to employee stock plans, including tax benefit	0	(1,169)	0	0	7,425	6,256
Stock-based compensation	0	3,521	0	0	0	3,521
Other comprehensive income	0	0	0	(262)	0	(262)
Ending Balance at Dec. 31, 2014	$ 497	$ 576,504	$ 423,956	$ (17,027)	$ (119,749)	$ 864,181