ACQUISITIONS (Details for Apartments.com) $ in Thousands			3 Months Ended		9 Months Ended
	Jun. 01, 2015 USD ($) distinct_intangible_asset	Apr. 02, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Apr. 01, 2014 USD ($) distinct_intangible_asset	Dec. 31, 2013 USD ($)
Business Acquisition [Line Items]
Goodwill			$ 1,249,945		$ 1,249,945		$ 1,138,805		$ 718,587
Apartments.com [Member]
Business Acquisition [Line Items]
Payments to acquire businesses		$ 587,104
Closing purchase price adjustments		2,104
Post closing purchase price adjustments		$ 2,886
Goodwill								$ 421,724
Goodwill tax deductible amount								$ 421,724
Business combination, acquisition related costs			$ 0	$ 0	$ 0	$ 1,375
Apartment Finder [Member]
Business Acquisition [Line Items]
Payments to acquire businesses	$ 172,706
Closing purchase price adjustments	2,706
Post closing purchase price adjustments	21
Goodwill	107,692
Goodwill tax deductible amount	$ 0
Customer Contracts [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets					10 years
Customer Contracts [Member] | Apartments.com [Member]
Business Acquisition [Line Items]
Number of distinct intangible assets | distinct_intangible_asset								1
Estimated useful life of acquired assets		10 years
Customer Contracts [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Number of distinct intangible assets | distinct_intangible_asset	3
Estimated useful life of acquired assets	10 years
Developed Technology Rights [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets					5 years
Developed Technology Rights [Member] | Apartments.com [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		1 year
Developed Technology Rights [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	5 months
Trade Names and Other Intangible Assets [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets					12 years
Trade Names and Other Intangible Assets [Member] | Apartments.com [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		13 years
Trade Names and Other Intangible Assets [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	9 years
Building Photography [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets					4 years
Building Photography [Member] | Apartments.com [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		3 years
Building Photography [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	5 months