BUSINESS COMBINATIONS - AEP Acquisition (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Aug. 31, 2019	Dec. 31, 2018	Jul. 01, 2018
Business Acquisition [Line Items]
Accounts Receivable				$ 45,875
Goodwill	$ 705,707		$ 734,607	700,286
Total assets acquired				2,130,448
Accounts Payable				13,089
Other Current Liabilities				9,185
Total liabilities assumed				405,763
Total net assets acquired				$ 1,724,685
AEP
Business Acquisition [Line Items]
Cash		$ 43
Accounts Receivable		116
Other Prepayments and Current Assets		53
Goodwill		1,843
Other Noncurrent Assets		2,400
Total assets acquired		4,455
Accounts Payable		11
Other Current Liabilities		449
Total liabilities assumed		460
Total net assets acquired		$ 3,995