Consolidated Statement of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]
Beginning Balance at Dec. 31, 2017	$ 141,189		$ 224	$ 181,910	$ 123,010		$ (161,943)	$ (2,012)
Beginning Balance (ASU No. 2014-09 [Member]) at Dec. 31, 2017		$ 3,803				$ 3,829			$ (26)
Beginning 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
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
Issuance of common stock under stock plans, including tax effects	2,800		$ 3	2,797
Issuance of common stock under stock plans, including tax effects, Shares			373
Stock-based compensation expense	10,877			10,877
Net income (loss)	9,990				9,990
Net change in interest rate swap, net of tax	(717)							(717)
Foreign currency translation	4,884							4,884
Ending Balance at Dec. 31, 2020	$ 185,766		$ 236	$ 230,128	$ 127,981		$ (171,889)	$ (690)
Ending Balance (ASU No. 2016-13 [Member]) at Dec. 31, 2020		$ (156)				$ (156)
Ending Balance, Shares at Dec. 31, 2020			23,648				4,631