COMMITMENTS, CONTINGENCIES AND REGULATORY MATTERS - Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Right-to-use assets	$ 29,074	$ 0			$ 42,100
Lease obligation liabilities					$ 45,500
Sublease income	$ 1,700	$ 1,600	$ 1,300
Minimum
Lessee, Lease, Description [Line Items]
Lease term				1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease term				6 years