CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - UNAUDITED - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Earnings
Balance, beginning of period at Dec. 31, 2019	$ 396,662	$ 696	$ 454,663	$ (867,817)	$ (39,503)	$ 848,623
Balance, beginning of period, shares at Dec. 31, 2019		32,891
Net income	21,514					21,514
Unrealized gain on short-term investments, net of tax	(24)				(24)
Foreign currency translation adjustments	(15,084)				(15,084)
Total comprehensive income	6,406
Repurchase of common stock	(13,965)	$ (2)	(7,555)	(6,408)
Repurchase of common stock, shares		(299)
Issuance of common stock pursuant to employee stock purchase plan	564		564
Issuance of common stock pursuant to employee stock purchase plan, shares		14
Issuance of restricted common stock pursuant to stock-based compensation plans		$ 5	(5)
Issuance of restricted common stock pursuant to stock-based compensation plans, shares		476
Cancellation of restricted common stock issued pursuant to stock-based compensation plans, shares		(7)
Stock-based compensation expense	4,857		4,857
Dividends	(7,693)					(7,693)
Balance, ending of period at Mar. 31, 2020	386,831	$ 699	452,524	(874,225)	(54,611)	862,444
Balance, ending of period, shares at Mar. 31, 2020		33,075
Balance, beginning of period at Dec. 31, 2020	$ 422,395	$ 700	470,557	(894,126)	(31,138)	876,402
Balance, beginning of period, shares at Dec. 31, 2020	32,713	32,713
Net income	$ 19,631					19,631
Unrealized gain on short-term investments, net of tax	(6)				(6)
Foreign currency translation adjustments	(355)				(355)
Total comprehensive income	19,270
Repurchase of common stock	(11,721)	$ (1)	(5,202)	(6,518)
Repurchase of common stock, shares		(252)
Issuance of common stock pursuant to employee stock purchase plan	619		619
Issuance of common stock pursuant to employee stock purchase plan, shares		16
Issuance of restricted common stock pursuant to stock-based compensation plans		$ 5	(5)
Issuance of restricted common stock pursuant to stock-based compensation plans, shares		487
Cancellation of restricted common stock issued pursuant to stock-based compensation plans, shares		(1)
Stock-based compensation expense	5,395		5,395
Dividends	(8,243)					(8,243)
Balance, ending of period at Mar. 31, 2021	$ 427,715	$ 704	$ 471,364	$ (900,644)	$ (31,499)	$ 887,790
Balance, ending of period, shares at Mar. 31, 2021	32,963	32,963