CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, except Share data	Total	Common Stock	Common Stock Warrants	Paid-In Capital	Treasury Stock	Accumulated Earnings	Accumulated Other Comprehensive Income
Balance, beginning of period at Dec. 31, 2011		$ 645		$ 449,376	$ (714,893)	$ 543,995	$ (4,409)
Balance, beginning of period, shares at Dec. 31, 2011		33,822,000
Issuance of restricted common stock pursuant to employee stock-based compensation plans		8		(8)
Repurchase and cancellation of common stock pursuant to employee stock-based compensation plans				(3,208)
Issuance of common stock pursuant to employee stock purchase plan				1,394
Exercise of stock options				502
Stock-based compensation expense				13,431
Stock-based compensation income tax benefits				10
Repurchase of common stock pursuant to Board - approved stock repurchase program	(13,349)				(13,350)
Net income	48,879					48,879
Net unrealized gains (losses) on short-term investments							2
Net unrealized gains on pension plan and prior service costs							33
Net unrealized gains (losses) on change in fair value of interest rate swap contracts	(40)						(40)
Foreign currency translation adjustments	4,272						4,272
Repurchase of common stock pursuant to Board -approved stock repurchase program, shares	(823,000)	(823,000)
Issuance of common stock pursuant to employee stock purchase plan, shares		94,000
Exercise of stock options, shares		40,000
Issuance of restricted common stock pursuant to employee stock-based compensation plans, shares		873,000
Cancellation of unvested restricted common stock pursuant to employee stock-based compensation plans, shares		(77,000)
Repurchase and cancellation of common stock pursuant to employee stock-based compensation plans, shares	(197,000)	(195,000)
Balance, end of period at Dec. 31, 2012	326,639	653		461,497	(728,243)	592,874	(142)
Balance, end of period, shares at Dec. 31, 2012		33,734,000
Issuance of restricted common stock pursuant to employee stock-based compensation plans		8		(8)
Repurchase and cancellation of common stock pursuant to employee stock-based compensation plans		(3)		(5,346)
Issuance of common stock pursuant to employee stock purchase plan				1,347
Exercise of stock options				244
Stock-based compensation expense				14,796
Stock-based compensation income tax benefits				660
Repurchase of common stock pursuant to Board - approved stock repurchase program	(10,129)				(10,129)
Net income	51,351					51,351
Declaration of cash dividends						(15,214)
Net unrealized gains (losses) on short-term investments							38
Net unrealized gains on pension plan and prior service costs							1,761
Net unrealized gains (losses) on change in fair value of interest rate swap contracts	560						560
Foreign currency translation adjustments	(600)						(600)
Repurchase of common stock pursuant to Board -approved stock repurchase program, shares	(500,000)	(500,000)
Issuance of common stock pursuant to employee stock purchase plan, shares		68,000
Exercise of stock options, shares		20,000
Issuance of restricted common stock pursuant to employee stock-based compensation plans, shares		840,000
Cancellation of unvested restricted common stock pursuant to employee stock-based compensation plans, shares		(153,000)
Repurchase and cancellation of common stock pursuant to employee stock-based compensation plans, shares	(264,000)	(264,000)
Balance, end of period at Dec. 31, 2013	366,104	658		473,190	(738,372)	629,011	1,617
Balance, end of period, shares at Dec. 31, 2013	33,745,000	33,745,000	0
Issuance of restricted common stock pursuant to employee stock-based compensation plans		11		(11)
Repurchase and cancellation of common stock pursuant to employee stock-based compensation plans		(2)		(6,925)
Issuance of common stock warrants, granted to Comcast (exercise price of $26.68 per warrant)			6,694
Issuance of common stock pursuant to employee stock purchase plan				1,394
Stock-based compensation expense				16,706
Stock-based compensation income tax benefits				2,060
Repurchase of common stock pursuant to Board - approved stock repurchase program	(19,106)				(19,106)
Net income	36,959					36,959
Declaration of cash dividends						(21,164)
Net unrealized gains (losses) on short-term investments							(35)
Net unrealized gains (losses) on change in fair value of interest rate swap contracts	98						98
Foreign currency translation adjustments	(15,060)						(15,060)
Repurchase of common stock pursuant to Board -approved stock repurchase program, shares	(733,000)	(733,000)
Issuance of common stock pursuant to employee stock purchase plan, shares		61,000
Issuance of restricted common stock pursuant to employee stock-based compensation plans, shares		1,261,000
Cancellation of unvested restricted common stock pursuant to employee stock-based compensation plans, shares		(137,000)
Repurchase and cancellation of common stock pursuant to employee stock-based compensation plans, shares	(252,000)	(252,000)
Balance, end of period at Dec. 31, 2014	$ 367,723	$ 667	$ 6,694	$ 486,414	$ (757,478)	$ 644,806	$ (13,380)
Balance, end of period, shares at Dec. 31, 2014	33,945,000	33,945,000	2,851,000