SEGMENTS, GEOGRAPHIC INFORMATION AND SIGNIFICANT CUSTOMERS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 business_segments	Jun. 30, 2013
Segment Reporting Information [Line Items]
Number of Business Segments (in segments)			2
Revenue	$ 137,380	$ 128,094	$ 283,293	$ 262,577
Segment income from operations	46,834	50,556	102,075	104,804
Corporate Expenses	(8,208)	(6,760)	(18,055)	(13,632)
Share-based Compensation	(4,828)	(4,833)	(9,577)	(9,350)
Amortization of Acquired Intangible Assets	(3,606)	(3,549)	(8,144)	(7,100)
Income from operations	27,714	33,428	61,512	70,751
Depreciation and leasehold amortization	3,204	3,009	6,272	6,008
Cost of Sales [Member]
Segment Reporting Information [Line Items]
Amortization of Acquired Intangible Assets	(2,478)	(1,986)	(4,787)	(3,971)
Operating Expense [Member]
Segment Reporting Information [Line Items]
Amortization of Acquired Intangible Assets	(3,606)	(3,549)	(8,144)	(7,100)
Affiliate Marketing [Member]
Segment Reporting Information [Line Items]
Revenue	40,632	36,622	83,096	74,933
Segment income from operations	24,755	22,584	50,867	45,509
Depreciation and leasehold amortization	328	326	692	667
Media [Member]
Segment Reporting Information [Line Items]
Revenue	96,748	91,490	200,210	187,746
Segment income from operations	22,079	27,972	51,208	59,295
Depreciation and leasehold amortization	2,540	2,386	4,918	4,781
Inter-regional Elimination [Member]
Segment Reporting Information [Line Items]
Revenue	0	(18)	(13)	(102)
Segment income from operations	0	0	0	0
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Depreciation and leasehold amortization	$ 336	$ 297	$ 662	$ 560