INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	$ 275,750	$ 288,911
Capitalized Product Development Costs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	2,173	2,173
Finite-lived intangible assets, accumulated amortization	(2,173)	(2,173)
Finite-lived intangible assets, net	$ 0	0
Weighted-average amortization period	4 years
Acquired building photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 9,087	9,035
Finite-lived intangible assets, accumulated amortization	(8,949)	(8,809)
Finite-lived intangible assets, net	$ 138	226
Weighted-average amortization period	2 years
Acquired database technology
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 101,887	103,128
Finite-lived intangible assets, accumulated amortization	(85,963)	(85,344)
Finite-lived intangible assets, net	$ 15,924	17,784
Weighted-average amortization period	5 years
Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 339,685	339,574
Finite-lived intangible assets, accumulated amortization	(207,199)	(199,405)
Finite-lived intangible assets, net	$ 132,486	140,169
Weighted-average amortization period	10 years
Acquired trade names and other intangible assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 190,614	190,717
Finite-lived intangible assets, accumulated amortization	(63,412)	(59,985)
Finite-lived intangible assets, net	$ 127,202	$ 130,732
Weighted-average amortization period	12 years