COMMITMENTS AND CONTINGENCIES - Commitments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Total commitments	$ 1,909,084	$ 1,677,615
Less: funded commitments	(1,692,894)	(1,534,743)
Total unfunded commitments	$ 216,190	$ 142,872