ACQUISITIONS (Details) - USD ($)					6 Months Ended		12 Months Ended
	Jun. 24, 2020	Feb. 11, 2020	Oct. 22, 2019	Jun. 12, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jul. 29, 2020	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill					$ 2,009,117,000		$ 1,882,020,000		$ 1,611,535,000
Cash paid for acquisitions, net of cash acquired					184,502,000	$ 13,721,000
Goodwill acquired					135,878,000		$ 267,804,000
Ten-X [Member]
Business Acquisition [Line Items]
Aggregate purchase price	$ 187,000,000
Goodwill	135,446,000
Transaction costs					3,000,000
RentPath [Member]
Business Acquisition [Line Items]
Aggregate purchase price		$ 588,000,000
Restricted cash					$ 59,000,000
RentPath [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Maximum potential payment for agreement extension								$ 7,500,000
STR Inc and STR Global Ltd [Member]
Business Acquisition [Line Items]
Aggregate purchase price			$ 435,000,000
Goodwill			261,868,000
Transaction costs			2,000,000
Employee retention bonus			$ 15,000,000
Requisite service period			1 year
Off Campus Partners [Member]
Business Acquisition [Line Items]
Cash paid for acquisitions, net of cash acquired				$ 16,000,000
Initial payments to acquire businesses, net of cash acquired				14,000,000
Goodwill acquired				8,000,000
Finite-lived intangible assets acquired				$ 9,000,000
North America [Member] | Ten-X [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets acquired	$ 58,000,000
North America [Member] | STR Inc and STR Global Ltd [Member]
Business Acquisition [Line Items]
Goodwill			$ 159,000,000
Finite-lived intangible assets acquired			131,000
International [Member] | STR Inc and STR Global Ltd [Member]
Business Acquisition [Line Items]
Goodwill			103,000,000
Finite-lived intangible assets acquired			$ 47,000