COMMITMENTS AND CONTINGENCIES (Details) (USD $)	1 Months Ended	12 Months Ended					0 Months Ended
	May 31, 2011 class_action_lawsuits	Dec. 31, 2013 current_litigation_matters	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 LoopNet Stockholders [Member]	Dec. 31, 2013 Civix [Member]	Feb. 16, 2012 LoopNet [Member] CoStar Group [Member] New Term Loan [Member]	Feb. 16, 2012 LoopNet [Member] CoStar Group [Member] New Revolving Credit Facility [Member]
Operating Leases Rent Expense [Abstract]
Rent expense for operating leases		$ 18,300,000	$ 16,700,000	$ 13,300,000
Future Minimum Lease Payments [Abstract]
2014		17,004,000
2015		15,128,000
2016		14,104,000
2017		14,317,000
2018		13,916,000
2019 and thereafter		69,475,000
Total future minimum lease payments		143,944,000
Business Acquisition [Line Items]
Debt instrument borrowing capacity							175,000,000	50,000,000
Term of loan (in years)							5 years	5 years
Number of class action lawsuits brought by alleged LoopNet stockholders	3
Loss contingency accrual					200,000	600,000
Loss contingency, estimated damages sought		3,700,000
Estimate of possible loss in excess of amount accrued						$ 3,100,000
Number of minimum of current litigation matters (in claims)		1