Consolidated Statements of Shareholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2011	$ 290,150	$ 310	$ 373,591	$ 104,077	$ (181,000)	$ (6,828)
Beginning Balance, Shares at Dec. 31, 2011		30,962			8,215
Issuance of common stock under stock plans, including tax effects	10,379	5	10,374
Issuance of common stock under stock plans, including tax effects, Shares		489
Stock-based compensation expense	5,397		5,397
Purchase of common stock	(29,843)				(29,843)
Purchase of common stock, Shares					943
Dividends paid on common shares	(12,588)			(12,588)
Net income	26,296			26,296
Net change in marketable investments, net of tax	(3)					(3)
Foreign currency translation	7,419					7,419
Ending Balance at Dec. 31, 2012	297,207	315	389,362	117,785	(210,843)	588
Ending Balance, Shares at Dec. 31, 2012		31,451			9,158
Issuance of common stock under stock plans, including tax effects	17,118	7	17,111
Issuance of common stock under stock plans, including tax effects, Shares		724
Stock-based compensation expense	6,051		6,051
Purchase of common stock	(118,210)				(118,210)
Purchase of common stock, Shares					3,261
Retirement of treasury stock	(303,000)	(117)	(302,848)		302,965
Retirement of treasury stock, Shares	(11,700)	(11,684)			(11,684)
Dividends paid on common shares	(12,394)			(12,394)
Net income	13,024			13,024
Net change in marketable investments, net of tax	1,040					1,040
Foreign currency translation	826					826
Ending Balance at Dec. 31, 2013	204,662	205	109,676	118,415	(26,088)	2,454
Ending Balance, Shares at Dec. 31, 2013		20,491			735
Issuance of common stock under stock plans, including tax effects	7,826	4	7,822
Issuance of common stock under stock plans, including tax effects, Shares		365
Stock-based compensation expense	7,444		7,444
Purchase of common stock	(73,166)				(73,166)
Purchase of common stock, Shares					1,968
Dividends paid on common shares	(11,962)			(11,962)
Net income	10,865			10,865
Net change in marketable investments, net of tax	(90)					(90)
Foreign currency translation	(3,977)					(3,977)
Ending Balance at Dec. 31, 2014	$ 141,602	$ 209	$ 124,942	$ 117,318	$ (99,254)	$ (1,613)
Ending Balance, Shares at Dec. 31, 2014		20,856			2,703