ACQUISITION (Details for Apartment Finder)		12 Months Ended
	Jun. 01, 2015 USD ($) distinct_intangible_asset	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 1,254,866,000	$ 1,252,945,000	$ 1,138,805,000
Apartment Finder [Member]
Business Acquisition [Line Items]
Percentage of outstanding stock acquired	100.00%
Payments to acquire businesses	$ 173,000,000
Closing purchase price adjustments	3,000,000
Post closing purchase price adjustments	21,000
Goodwill	107,692,000
Goodwill tax deductible amount	$ 0
Acquired Trade Names and Other Intangible Assets [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		13 years
Acquired Trade Names and Other Intangible Assets [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	9 years
Acquired Customer Base [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		10 years
Acquired Customer Base [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
Acquired Database Technology [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		5 years
Acquired Database Technology [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	5 months
Acquired Building Photography [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		4 years
Acquired Building Photography [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	5 months