RELATED PARTY TRANSACTIONS - Summary of Due From and Due To Affiliates (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Due from Affiliates	$ 682,007	$ 554,349
Due to Affiliates	252,547	323,810
Portfolio Companies
Related Party Transaction [Line Items]
Due from Affiliates	102,183	129,594
Unconsolidated Investment Funds
Related Party Transaction [Line Items]
Due from Affiliates	571,470	415,907
Due to Affiliates	155,554	239,776
Related Entities
Related Party Transaction [Line Items]
Due from Affiliates	8,354	8,848
Due to KKR Holdings in connection with the tax receivable agreement
Related Party Transaction [Line Items]
Due to Affiliates	$ 96,993	$ 84,034