INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands		9 Months Ended
	Jun. 01, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net		$ 207,113		$ 238,318
Impairment of intangible assets, finite-lived		0	$ 2,778
Capitalized Product Development Costs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		2,275		2,243
Finite-lived intangible assets, accumulated amortization		(2,205)		(2,172)
Finite-lived intangible assets, net		$ 70		71
Weighted-average amortization period (in years}		4 years
Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		$ 17,375		17,677
Finite-lived intangible assets, accumulated amortization		(16,246)		(15,875)
Finite-lived intangible assets, net		$ 1,129		1,802
Weighted-average amortization period (in years}		4 years
Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		$ 78,332		77,905
Finite-lived intangible assets, accumulated amortization		(69,870)		(62,818)
Finite-lived intangible assets, net		$ 8,462		15,087
Weighted-average amortization period (in years}		5 years
Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		$ 221,385		221,409
Finite-lived intangible assets, accumulated amortization		(145,859)		(129,782)
Finite-lived intangible assets, net		$ 75,526		91,627
Weighted-average amortization period (in years}		10 years
Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		$ 153,736		153,910
Finite-lived intangible assets, accumulated amortization		(31,810)		(24,179)
Finite-lived intangible assets, net		$ 121,926		$ 129,731
Weighted-average amortization period (in years}		13 years
Apartments.com [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of intangible assets, finite-lived			1,000
Apartment Finder [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of intangible assets, finite-lived			$ 1,000
Apartment Finder [Member] | Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	5 months
Apartment Finder [Member] | Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	5 months
Apartment Finder [Member] | Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	10 years
Apartment Finder [Member] | Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	9 years
LoopNet [Member] | Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		15 years