BUSINESS COMBINATIONS - Assets Acquired and Liabilities assumed (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Apr. 22, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill	$ 961,602		$ 47,453
Saba Software, Inc.
Business Acquisition [Line Items]
Cash and cash equivalents		$ 49,471
Accounts receivable		58,764
Prepaid expenses and other current assets		13,020
Property and equipment		9,446
Operating right-of-use assets		16,700
Intangible assets		481,000
Goodwill		905,498
Other assets		2,698
Total assets		1,536,597
Accounts payable and accrued expenses		28,978
Deferred revenue		69,940
Operating lease liabilities		16,532
Deferred tax liabilities, net		46,472
Other liabilities		12,782
Total liabilities		174,704
Net assets acquired		$ 1,361,893