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
Balance, beginning of period at Dec. 31, 2013	$ 358,262	$ 658		$ 473,190	$ (738,372)	$ 1,617	$ 621,169
Balance, beginning of period, shares at Dec. 31, 2013		33,745
Net income	35,711						35,711
Unrealized gain (loss) on short-term investments, net of tax	(35)					(35)
Unrealized pension plan gains and prior service costs, net of tax						98
Foreign currency translation adjustments	(15,060)					(15,060)
Total comprehensive income, net of tax	20,714
Repurchase of common stock	(26,033)	$ (2)		(6,925)	(19,106)
Repurchase of common stock, shares		(985)
Issuance of common stock pursuant to employee stock purchase plan	1,394			1,394
Issuance of common stock pursuant to employee stock purchase plan, shares		61
Stock-based compensation income tax benefits	2,060			2,060
Issuance of restricted common stock pursuant to stock-based compensation plans		$ 11		(11)
Issuance of restricted common stock pursuant to stock-based compensation plans, shares		1,261
Cancellation of restricted common stock issued pursuant to stock-based compensation plans, shares		(137)
Stock-based compensation expense	16,706			16,706
Issuance of common stock warrants, granted to Comcast	6,694		$ 6,694
Declaration of cash dividends	(21,164)						(21,164)
Balance, ending of period at Dec. 31, 2014	358,633	$ 667	6,694	486,414	(757,478)	(13,380)	635,716
Balance, ending of period, shares at Dec. 31, 2014		33,945
Net income	62,567						62,567
Unrealized gain (loss) on short-term investments, net of tax	(103)					(103)
Foreign currency translation adjustments	(12,902)					(12,902)
Total comprehensive income, net of tax	49,562
Repurchase of common stock	(65,027)	$ (3)		(8,065)	(56,959)
Repurchase of common stock, shares		(2,103)
Issuance of common stock pursuant to employee stock purchase plan	1,547	$ 1		1,546
Issuance of common stock pursuant to employee stock purchase plan, shares		59
Stock-based compensation income tax benefits	2,185			2,185
Issuance of restricted common stock pursuant to stock-based compensation plans		$ 8		(8)
Issuance of restricted common stock pursuant to stock-based compensation plans, shares		728
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		(74)
Stock-based compensation expense	21,181			21,181
Issuance of common stock warrants, granted to Comcast	616		616
Declaration of cash dividends	(22,852)						(22,852)
Balance, ending of period at Dec. 31, 2015	$ 345,845	$ 672	7,310	503,254	(814,437)	(26,385)	675,431
Balance, ending of period, shares at Dec. 31, 2015	32,555	32,555
Net income	$ 62,882						62,882
Unrealized gain (loss) on short-term investments, net of tax	(62)					(62)
Foreign currency translation adjustments	(18,925)					(18,925)
Total comprehensive income, net of tax	43,895
Repurchase of common stock	(25,196)	$ (3)		(13,628)	(11,565)
Repurchase of common stock, shares		(662)
Issuance of common stock pursuant to employee stock purchase plan	1,547			1,547
Issuance of common stock pursuant to employee stock purchase plan, shares		44
Stock-based compensation income tax benefits	4,729			4,729
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		572
Cancellation of restricted common stock issued pursuant to stock-based compensation plans		$ (2)		2
Cancellation of restricted common stock issued pursuant to stock-based compensation plans, shares		(248)
Stock-based compensation expense	22,745			22,745
Issuance of common stock warrants, granted to Comcast	8,697		8,697
Issuance of convertible notes	9,816			9,816
Repurchase of convertible notes, net of tax	(97,410)			(97,410)
Debt conversion obligation reclassification	(39,841)			(39,841)
Declaration of cash dividends	(23,467)						(23,467)
Balance, ending of period at Dec. 31, 2016	$ 251,360	$ 672	$ 16,007	$ 391,209	$ (826,002)	$ (45,372)	$ 714,846
Balance, ending of period, shares at Dec. 31, 2016	32,261	32,261