Consolidated Statement of Shareholders' Equity - USD ($) shares in Thousands, $ 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, 2012	$ 297,207	$ 315	$ 389,362	$ 117,785	$ (210,843)	$ 588
Beginning 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
Repurchases of common stock	(118,210)				$ (118,210)
Repurchase 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
Repurchases of common stock	(73,166)				$ (73,166)
Repurchase 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
Issuance of common stock under stock plans, including tax effects	1,680	$ 2	1,678
Issuance of common stock under stock plans, including tax effects, Shares		207
Stock-based compensation expense	8,347		8,347
Repurchases of common stock	(20,931)				$ (20,931)
Repurchase of common stock, Shares					608
Dividends paid on common shares	(12,179)			(12,179)
Net income	11,996			11,996
Net change in marketable investments, net of tax	(26)					(26)
Foreign currency translation	(3,187)					(3,187)
Ending Balance at Dec. 31, 2015	$ 127,302	$ 211	$ 134,967	$ 117,135	$ (120,185)	$ (4,826)
Ending Balance, Shares at Dec. 31, 2015		21,063			3,311