RECEIVABLES, CONTRACT ASSETS, AND DEFERRED REVENUE - Summary of Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Receivables [Abstract]
Accounts receivable	$ 143,445	$ 215,827
Unbilled receivables	239,774	207,155
Long-term unbilled receivables	132,147	113,278
Total receivables	$ 515,366	$ 536,260

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant