INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands			12 Months Ended
	Jun. 01, 2015	Apr. 03, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 30, 2012
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net			$ 238,318	$ 241,622
Amortization of intangible assets			58,565	55,261	$ 27,563
Impairment of intangible assets, finite-lived			2,778	1,799	$ 0
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Amortization expense for 2016			43,000
Amortization expense for 2017			28,500
Amortization expense for 2018			20,300
Amortization expense for 2019			17,400
Amortization expense for 2020			15,800
Capitalized Product Development Costs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross			2,243	2,140
Finite-lived intangible assets, accumulated amortization			(2,172)	(2,140)
Finite-lived intangible assets, net			$ 71	0
Weighted-average amortization period (in years}			4 years
Acquired Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross			$ 17,677	14,943
Finite-lived intangible assets, accumulated amortization			(15,875)	(12,665)
Finite-lived intangible assets, net			$ 1,802	2,278
Weighted-average amortization period (in years}			4 years
Acquired Database Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross			$ 77,905	88,739
Finite-lived intangible assets, accumulated amortization			(62,818)	(60,498)
Finite-lived intangible assets, net			$ 15,087	28,241
Weighted-average amortization period (in years}			5 years
Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross			$ 221,409	199,826
Finite-lived intangible assets, accumulated amortization			(129,782)	(102,443)
Finite-lived intangible assets, net			$ 91,627	97,383
Weighted-average amortization period (in years}			10 years
Acquired Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross			$ 153,910	128,171
Finite-lived intangible assets, accumulated amortization			(24,179)	(14,451)
Finite-lived intangible assets, net			$ 129,731	$ 113,720
Weighted-average amortization period (in years}			12 years
LoopNet [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived acquired trade names and other intangible assets						$ 48,700
Apartments.com [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of intangible assets, finite-lived			$ 1,402
Apartments.com [Member] | Acquired Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		3 years
Apartments.com [Member] | Acquired Database Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		1 year
Apartments.com [Member] | Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		10 years
Apartments.com [Member] | Acquired Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		13 years
Apartment Finder [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of intangible assets, finite-lived			$ 1,376
Apartment Finder [Member] | Acquired Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	5 months
Apartment Finder [Member] | Acquired Database Technology [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] | Acquired Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	9 years