SEGMENTS AND GEOGRAPHIC INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 business_segments	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Number of Business Segments	4
Revenue	$ 560,155	$ 430,798	$ 422,723
Segment income from operations	192,914	147,738	139,191
Total Assets	880,711	613,567	566,562
Corporate expenses	(26,531)	(26,663)	(27,988)
Stock-based compensation	(14,022)	(7,944)	(8,869)
Amortization of Acquired Intangible Assets	(26,279)	(20,611)	(19,803)
Consolidated income from operations	126,082	92,520	82,531
Depreciation and leasehold amortization	8,027	6,620	7,554
Affiliate Marketing [Member]
Segment Reporting Information [Line Items]
Revenue	139,409	124,126	111,903
Segment income from operations	84,573	69,552	58,121
Total Assets	59,755	59,336	50,980
Depreciation and leasehold amortization	1,062	1,052	1,057
Media [Member]
Segment Reporting Information [Line Items]
Revenue	224,574	137,487	135,086
Segment income from operations	55,020	33,625	33,261
Total Assets	651,010	290,684	282,135
Depreciation and leasehold amortization	3,835	2,397	2,135
Owned and Operated Websites [Member]
Segment Reporting Information [Line Items]
Revenue	159,821	138,545	149,599
Segment income from operations	33,764	27,963	35,034
Total Assets	121,531	162,490	87,058
Depreciation and leasehold amortization	1,717	1,581	1,878
Technology [Member]
Segment Reporting Information [Line Items]
Revenue	37,031	31,889	27,686
Segment income from operations	19,557	16,598	12,775
Total Assets	12,041	10,639	6,951
Depreciation and leasehold amortization	1,079	865	1,017
Inter-segment revenue [Member]
Segment Reporting Information [Line Items]
Revenue	(680)	(1,249)	(1,551)
Segment income from operations	0	0	0
Total Assets	0	0	0
Corporate [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0
Segment income from operations	0	0	0
Total Assets	36,374	90,418	139,438
Depreciation and leasehold amortization	334	725	1,467
Cost of revenue [Member]
Segment Reporting Information [Line Items]
Amortization of Acquired Intangible Assets	(9,633)	(7,522)	(6,675)
Operating expenses [Member]
Segment Reporting Information [Line Items]
Amortization of Acquired Intangible Assets	$ (16,646)	$ (13,089)	$ (13,128)