INTANGIBLE ASSETS AND GOODWILL - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2020	Mar. 03, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 1,237,672,000		$ 1,237,672,000				$ 1,203,197,000	$ 17,279,000
Impairment losses			0	$ 0
Intangible asset impairment charge	209,666,000	$ 0	209,666,000	$ 0
Finite-lived intangible assets, gross	959,895,000		959,895,000				963,690,000
Finite-lived intangible assets, accumulated amortization	88,441,000		88,441,000				$ 20,411,000
Paradigm & Viomics
Finite-Lived Intangible Assets [Line Items]
Goodwill					$ 30,400,000	$ 30,431,000
Merger Agreement with Genomic Health, Inc.
Finite-Lived Intangible Assets [Line Items]
Genomic Health acquisition adjustment	4,044,000		4,044,000
In-process research and development
Finite-Lived Intangible Assets [Line Items]
Intangible asset impairment charge	200,000,000.0
In-process research and development | Armune Biosciences Agreement
Finite-Lived Intangible Assets [Line Items]
Intangible asset impairment charge	9,700,000		9,700,000
Finite-lived intangible assets, gross	12,200,000		12,200,000
Finite-lived intangible assets, accumulated amortization	$ 2,500,000		2,500,000
In-process research and development | Biocartis Agreement
Finite-Lived Intangible Assets [Line Items]
Intangible asset impairment charge			$ 200,000,000.0