CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - 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	Noncontrolling Interest
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	82,770						82,770
Unrealized gain on short-term investments, net of tax	14					14
Foreign currency translation adjustments	3,418					3,418
Total comprehensive income, net of tax	86,202
Repurchase of common stock	(30,525)			(5,068)	(25,457)
Repurchase of common stock, shares		(693)
Issuance of common stock pursuant to employee stock purchase plan	2,227			2,227
Issuance of common stock pursuant to employee stock purchase plan, shares		55
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		513
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		(142)
Stock-based compensation expense	19,919			19,919
Exercise of Comcast stock warrants	(12,911)		$ (9,082)	(3,829)
Dividends	(29,274)						(29,274)
Balance, ending of period at Dec. 31, 2019	396,662	$ 696		454,663	(867,817)	(39,503)	848,623
Balance, ending of period, shares at Dec. 31, 2019		32,891
Net income	58,711						58,711
Unrealized gain on short-term investments, net of tax	(3)					(3)
Foreign currency translation adjustments	8,368					8,368
Total comprehensive income, net of tax	67,076
Repurchase of common stock	(38,168)			(11,859)	(26,309)
Repurchase of common stock, shares		(878)
Issuance of common stock pursuant to employee stock purchase plan	2,523			2,523
Issuance of common stock pursuant to employee stock purchase plan, shares		68
Issuance of restricted common stock pursuant to stock-based compensation plans		$ 7		(7)
Issuance of restricted common stock pursuant to stock-based compensation plans, shares		672
Cancellation of restricted common stock issued pursuant to stock-based compensation plans	(3)	$ (3)
Cancellation of restricted common stock issued pursuant to stock-based compensation plans, shares		(40)
Stock-based compensation expense	25,237			25,237
Dividends	(30,932)						(30,932)
Balance, ending of period at Dec. 31, 2020	$ 422,395	$ 700		470,557	(894,126)	(31,138)	876,402
Balance, ending of period, shares at Dec. 31, 2020	32,713	32,713
Net income	$ 72,331						72,331
Unrealized gain on short-term investments, net of tax	(19)					(19)
Foreign currency translation adjustments	(7,196)					(7,196)
Total comprehensive income, net of tax	65,116
Repurchase of common stock	(42,238)			(6,258)	(35,980)
Repurchase of common stock, shares		(863)
Issuance of common stock pursuant to employee stock purchase plan	2,610			2,610
Issuance of common stock pursuant to employee stock purchase plan, shares		64
Issuance of restricted common stock pursuant to stock-based compensation plans		$ 6
Issuance of restricted common stock pursuant to stock-based compensation plans, shares		661
Cancellation of restricted common stock issued pursuant to stock-based compensation plans	(1)	$ (1)		(6)
Cancellation of restricted common stock issued pursuant to stock-based compensation plans, shares		(80)
Stock-based compensation expense	21,400			21,400
Dividends	(32,673)						(32,673)
Noncontrolling interest related to business combination	3,635							$ 3,635
Balance, ending of period at Dec. 31, 2021	$ 440,244	$ 705		$ 488,303	$ (930,106)	$ (38,353)	$ 916,060	$ 3,635
Balance, ending of period, shares at Dec. 31, 2021	32,495	32,495