LOANS - Corporate Debt Amortized Costs Basis by Risk Rating and Vintage Year (Details) - Corporate Loans $ in Thousands	Mar. 31, 2020 USD ($)
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Total	$ 2,150,699
2020	255,908
2019	634,178
2018	783,148
2017	330,223
2016	74,876
2015	48,235
Revolvers	24,131
Accrued interest receivable	9,900
Performing
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Total	826,447
2020	22,285
2019	319,686
2018	286,358
2017	158,446
2016	29,957
2015	0
Revolvers	9,715
Closely Monitored
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Total	966,454
2020	233,623
2019	257,888
2018	325,885
2017	100,588
2016	21,932
2015	14,198
Revolvers	12,340
Special Mention
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Total	138,129
2020	0
2019	53,671
2018	17,441
2017	30,904
2016	0
2015	34,037
Revolvers	2,076
Substandard
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Total	215,372
2020	0
2019	2,933
2018	149,167
2017	40,285
2016	22,987
2015	0
Revolvers	0
Doubtful
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Total	4,297
2020	0
2019	0
2018	4,297
2017	0
2016	0
2015	0
Revolvers	0
Loss
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Total	0
2020	0
2019	0
2018	0
2017	0
2016	0
2015	0
Revolvers	$ 0