INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	$ 195,965	$ 238,318
Amortization of intangible assets	46,000	59,000	$ 55,000
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Amortization expense for 2017	33,000
Amortization expense for 2018	24,000
Amortization expense for 2019	21,000
Amortization expense for 2020	19,000
Amortization expense for 2021	18,000
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	(2,217)	(2,172)
Finite-lived intangible assets, net	$ 58	71
Weighted-average amortization period (in years}	4 years
Acquired Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 17,271	17,677
Finite-lived intangible assets, accumulated amortization	(16,351)	(15,875)
Finite-lived intangible assets, net	$ 920	1,802
Weighted-average amortization period (in years}	4 years
Acquired Database Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 78,151	77,905
Finite-lived intangible assets, accumulated amortization	(72,691)	(62,818)
Finite-lived intangible assets, net	$ 5,460	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	$ 220,749	221,409
Finite-lived intangible assets, accumulated amortization	(150,445)	(129,782)
Finite-lived intangible assets, net	$ 70,304	91,627
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	$ 153,607	153,910
Finite-lived intangible assets, accumulated amortization	(34,384)	(24,179)
Finite-lived intangible assets, net	$ 119,223	$ 129,731
Weighted-average amortization period (in years}	13 years
LoopNet [Member] | Acquired Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	15 years