INCOME TAXES AND RELATED PAYMENTS (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) company	Dec. 31, 2040 USD ($)	Dec. 31, 2037 USD ($)	Dec. 31, 2036 USD ($)	Dec. 31, 2035 USD ($)	Dec. 31, 2034 USD ($)	Dec. 31, 2029 USD ($)
Income Tax Disclosure [Abstract]
Number of wholly-owned subsidiaries | company	2
Decreases resulting from settlements with taxing authorities	$ 3,000
Percentage of cash savings	85.00%
Forecast
Tax Receivable Agreement [Line Items]
Expected payments to unitholders under tax receivable agreement		$ 187,872
2007 private offering | Forecast
Tax Receivable Agreement [Line Items]
Expected payments to unitholders under tax receivable agreement							$ 13,396
Initial public offering | Forecast
Tax Receivable Agreement [Line Items]
Expected payments to unitholders under tax receivable agreement						$ 32,411
Offering | Forecast
Tax Receivable Agreement [Line Items]
Expected payments to unitholders under tax receivable agreement		$ 32,330	$ 29,446	$ 34,640	$ 45,649