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, 2017	$ 342,746	$ 689	$ 9,082	$ 427,091	$ (814,732)	$ (28,822)	$ 749,438
Balance, beginning of period, shares at Dec. 31, 2017		33,516
Net income	14,014						14,014
Unrealized gain (loss) on short-term investments, net of tax	(94)					(94)
Foreign currency translation adjustments	7,710					7,710
Total comprehensive income, net of tax	21,630
Repurchase of common stock	(11,920)			(6,218)	(5,702)
Repurchase of common stock, shares		(255)
Issuance of common stock pursuant to employee stock purchase plan	484			484
Issuance of common stock pursuant to employee stock purchase plan, shares		14
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		458
Cancellation of restricted common stock issued pursuant to stock-based compensation plans		$ (1)		1
Cancellation of restricted common stock issued pursuant to stock-based compensation plans, shares		(59)
Stock-based compensation expense	4,572			4,572
Declaration of cash dividends	(6,999)						(6,999)
Adjustments due to adoption of new accounting standards	7,562						7,562
Balance, ending of period at Mar. 31, 2018	358,075	$ 692	9,082	425,926	(820,434)	(21,206)	764,015
Balance, ending of period, shares at Mar. 31, 2018		33,674
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	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
Declaration of cash 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	33,280