INCOME TAXES (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Income Tax Contingency [Line Items]
Income tax expense (benefit)		$ (1,300)	$ (500)	$ (7,400)	$ 3,000	$ 3,300
Deferred income tax expense (benefit)		3,500	$ 1,000	6,700	$ 1,500
Deferred tax asset related to capital losses		6,300		$ 6,300
Fees and other income						2,500
Applicable cash savings				85.00%
Applicable cash savings available to entity				15.00%
Amount payable pursuant to tax receivable agreement	[1]	1,559		$ 1,559		1,570
Other assets
Income Tax Contingency [Line Items]
Deferred tax liabilities		4,100		4,100
Deferred tax asset						2,300
Accrued Liabilities
Income Tax Contingency [Line Items]
Unrecognized tax benefits		900		900		800
Amount Payable Pursuant to Tax Receivable Agreement
Income Tax Contingency [Line Items]
Amount payable pursuant to tax receivable agreement		$ 1,600		$ 1,600		$ 1,600

[1] Includes amounts relating to consolidated variable interest entities. See Note 3.