Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3521-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3044-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=123431023&loc=SL98516268-108586

Name:	us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, CASH RECONCILIATION (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Cash Reconciliation [Line Items]
Cash, cash equivalents and restricted cash	$ 3,761,587	$ 3,693,813
Restricted cash	0	62,099
Cash, cash equivalents and restricted cash	3,761,587	3,755,912	$ 3,867,805	$ 1,070,731
RentPath termination fee held in escrow under the terms of the Asset Purchase Agreement
Cash Reconciliation [Line Items]
Restricted cash	0	58,750
Other restricted cash related to acquisitions
Cash Reconciliation [Line Items]
Restricted cash	$ 0	$ 3,349