BUSINESS COMBINATIONS - Purchase Price Allocation (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 02, 2018
Preliminary Recording of Assets Acquired and Liabilities Assumed
Goodwill	$ 955,881	$ 955,881	$ 956,029
ABILITY Network
Preliminary Recording of Assets Acquired and Liabilities Assumed
Cash and cash equivalents				$ 23,850
Accounts receivable				16,739
Income tax receivable				688
Prepaid expenses and other current assets				3,025
Property and equipment				3,095
Goodwill				770,949
Intangible assets				490,000
Other assets				1,252
Accounts payable and accrued expenses				(6,863)
Deferred revenue				(7,000)
Other current liabilities				(507)
Other liabilities				(5,291)
Deferred tax liabilities				(98,887)
Total consideration transferred				$ 1,191,050