INVESTMENT OPERATIONS - Schedule of Fair Value (Proceeds) and Gains/Losses Realized on Securities Sold in an Unrealized Gail/Loss Position (Details) - USD ($) $ in Thousands	1 Months Ended	11 Months Ended	12 Months Ended
	Jan. 31, 2015	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Fair value (proceeds)		$ 948,774	$ 879,181	$ 1,194,808
Gains realized		8,735	18,868	42,058
Fair value (proceeds)		178,415	185,157	85,835
Losses realized		$ (8,463)	$ (8,257)	$ (9,783)
Predecessor
Investment [Line Items]
Fair value (proceeds)	$ 172,551
Gains realized	6,920
Fair value (proceeds)	435
Losses realized	$ (29)