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, 2012	$ 324,880	$ 653		$ 461,497	$ (728,243)	$ (142)	$ 591,115
Balance, beginning of period, shares at Dec. 31, 2012		33,734
Net income	45,268						45,268
Unrealized gain (loss) on short-term investments, net of tax						38
Unrealized pension plan gains and prior service costs, net of tax						1,761
Unrealized gain on change in fair value of interest rate swap contracts, net of tax	560					560
Foreign currency translation adjustments	(600)					(600)
Total comprehensive income, net of tax	47,027
Repurchase of common stock	(15,478)	$ (3)		(5,346)	(10,129)
Repurchase of common stock, shares		(764)
Issuance of common stock pursuant to employee stock purchase plan	1,347			1,347
Issuance of common stock pursuant to employee stock purchase plan, shares		68
Exercise of stock options	244			244
Exercise of stock options, shares		20
Stock-based compensation income tax benefits	660			660
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		840
Cancellation of restricted common stock issued pursuant to stock-based compensation plans, shares		(153)
Stock-based compensation expense	14,796			14,796
Declaration of cash dividends	(15,214)						(15,214)
Balance, ending of period at Dec. 31, 2013	358,262	$ 658		473,190	(738,372)	1,617	621,169
Balance, ending 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)
Unrealized pension plan gains and prior service costs, net of tax						98
Unrealized gain on change in fair value of interest rate swap contracts, 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	33,945
Net income	$ 62,567						62,567
Unrealized gain (loss) on short-term investments, net of tax						(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	(1,800)	(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