CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - UNAUDITED - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Common Stock Warrants	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Earnings
Balance, beginning of period at Dec. 31, 2018	$ 361,024	$ 693	$ 9,082	$ 441,417	$ (842,360)	$ (42,935)	$ 795,127
Balance, beginning of period, shares at Dec. 31, 2018		33,158
Net income	19,251						19,251
Unrealized gain (loss) on short-term investments, net of tax	18					18
Foreign currency translation adjustments	3,847					3,847
Total comprehensive income, net of tax	23,116
Repurchase of common stock	(13,424)			(4,134)	(9,290)
Repurchase of common stock, shares		(352)
Issuance of common stock pursuant to employee stock purchase plan	512			512
Issuance of common stock pursuant to employee stock purchase plan, shares		15
Issuance of restricted common stock pursuant to stock-based compensation plans		$ 4		(4)
Issuance of restricted common stock pursuant to stock-based compensation plans, shares		462
Cancellation of restricted common stock issued pursuant to stock-based compensation plans, shares		(3)
Stock-based compensation expense	3,693			3,693
Dividends	(7,411)						(7,411)
Balance, ending of period at Mar. 31, 2019	367,510	$ 697	$ 9,082	441,484	(851,650)	(39,070)	806,967
Balance, ending of period, shares at Mar. 31, 2019		33,280
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	32,891
Net income	$ 21,514						21,514
Unrealized gain (loss) on short-term investments, net of tax	(24)					(24)
Foreign currency translation adjustments	(15,084)					(15,084)
Total comprehensive income, net of tax	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	33,075