INCOME TAXES (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Tax Contingency [Line Items]
Income tax expense (benefit)		$ 400	$ 7,200	$ (6,900)	$ 10,200	$ 3,300
Deferred income tax expense (benefit)		700	$ (6,000)	7,400	$ (4,500)
Deferred tax asset related to capital losses		10,000		$ 10,000
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		4,700		4,700
Deferred tax asset						2,300
Accrued Liabilities
Income Tax Contingency [Line Items]
Unrecognized tax benefits		200		200		800
Amount of unrecognized tax benefit released due to statue of limitations				600
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 10.