INTANGIBLES AND OTHER ASSETS (Details) (USD $)	12 Months Ended					12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			0 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Capitalized Product Development Costs [Member]	Dec. 31, 2012 Capitalized Product Development Costs [Member]	Dec. 31, 2013 Building Photography [Member]	Dec. 31, 2012 Building Photography [Member]	Dec. 31, 2013 Acquired Database Technology [Member]	Dec. 31, 2012 Acquired Database Technology [Member]	Dec. 31, 2013 Acquired Customer Base [Member]	Dec. 31, 2012 Acquired Customer Base [Member]	Dec. 31, 2013 Acquired Trade Names and Other [Member]	Dec. 31, 2012 Acquired Trade Names and Other [Member]	Apr. 30, 2012 LoopNet [Member]	Apr. 30, 2012 LoopNet [Member] Acquired Database Technology [Member]	Apr. 30, 2012 LoopNet [Member] Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross				$ 2,140,000	$ 2,140,000	$ 13,743,000	$ 12,474,000	$ 77,368,000	$ 77,328,000	$ 130,960,000	$ 130,683,000	$ 59,336,000	$ 59,255,000
Finite-lived intangible assets, accumulated amortization				(2,029,000)	(1,838,000)	(12,005,000)	(11,639,000)	(41,073,000)	(29,673,000)	(74,734,000)	(59,218,000)	(9,234,000)	(8,880,000)
Finite-lived intangible assets, net	144,472,000	170,632,000		111,000	302,000	1,738,000	835,000	36,295,000	47,655,000	56,226,000	71,465,000	50,102,000	50,375,000
Weighted-average amortization period (in years}				4 years		5 years		5 years		10 years		7 years			5 years	10 years
Acquired trade names and other														48,700,000
Amortization of Intangible Assets	27,563,000	22,699,000	4,417,000
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Amortization expense for 2014	23,500,000
Amortization expense for 2015	20,800,000
Amortization expense for 2016	18,900,000
Amortization expense for 2017	10,000,000
Amortization expense for 2018	$ 5,100,000