COMMITMENTS, CONTINGENCIES AND REGULATORY MATTERS - Leases (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Right-to-use assets	$ 26,028		$ 26,028		$ 42,100	$ 0
Lease obligation liabilities					$ 45,500
Sublease income	$ 500	$ 400	$ 1,300	$ 1,200
Minimum
Lessee, Lease, Description [Line Items]
Lease term	1 year		1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease term	6 years		6 years