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, 2016	$ 150,036	$ 217	$ 157,569	$ 121,799	$ (121,976)	$ (7,573)
Beginning Balance, Shares at Dec. 31, 2016		21,719			3,358
Issuance of common stock under stock plans, including tax effects	15,979	$ 7	15,972
Issuance of common stock under stock plans, including tax effects, Shares		713
Cumulative effect adjustment due to adoption of new accounting pronouncements	(419)		(121)	(298)
Stock-based compensation expense	8,490		8,490
Repurchases of common stock	(39,967)				$ (39,967)
Repurchase of common stock, Shares					1,033
Dividends paid on common shares	(13,631)			(13,631)
Net income (loss)	15,140			15,140
Net change in marketable investments, net of tax	(32)					(32)
Foreign currency translation	5,593					5,593
Ending Balance at Dec. 31, 2017	141,189	$ 224	181,910	123,010	$ (161,943)	(2,012)
Ending Balance, Shares at Dec. 31, 2017		22,432			4,391
Issuance of common stock under stock plans, including tax effects	10,492	$ 6	10,486
Issuance of common stock under stock plans, including tax effects, Shares		519
Cumulative effect adjustment due to adoption of new accounting pronouncements	3,803			3,829		(26)
Stock-based compensation expense	8,300		8,300
Repurchases of common stock	(9,946)				$ (9,946)
Repurchase of common stock, Shares					240
Dividends paid on common shares	(14,502)			(14,502)
Net income (loss)	15,380			15,380
Net change in marketable investments, net of tax	141					141
Foreign currency translation	(3,257)					(3,257)
Ending Balance at Dec. 31, 2018	151,600	$ 230	200,696	127,717	$ (171,889)	(5,154)
Ending Balance, Shares at Dec. 31, 2018		22,951			4,631
Issuance of common stock under stock plans, including tax effects	4,077	$ 3	4,074
Issuance of common stock under stock plans, including tax effects, Shares		324
Stock-based compensation expense	11,684		11,684
Net income (loss)	(9,570)			(9,570)
Net change in interest rate swap, net of tax	(104)					(104)
Foreign currency translation	401					401
Ending Balance at Dec. 31, 2019	$ 158,088	$ 233	$ 216,454	$ 118,147	$ (171,889)	$ (4,857)
Ending Balance, Shares at Dec. 31, 2019		23,275			4,631