LOANS - Commercial Real Estate Amortized Cost Basis by Risk Rating and Vintage (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) loan	Mar. 31, 2019 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Loan loss provision	$ 99,326	$ 5,703
Commercial Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,563,134
2020	148,414
2019	547,245
2018	408,844
2017	238,163
2016	69,007
Prior	151,461
Accrued interest receivable	4,600
Performing | Commercial Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total	446,226
2020	89,647
2019	159,384
2018	103,547
2017	12,444
2016	0
Prior	81,204
Closely Monitored | Commercial Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total	501,717
2020	31,657
2019	265,728
2018	29,432
2017	105,893
2016	69,007
Prior	0
Special Mention | Commercial Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total	431,515
2020	27,110
2019	122,133
2018	212,015
2017	0
2016	0
Prior	70,257
Substandard | Commercial Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total	85,390
2020	0
2019	0
2018	30,390
2017	55,000
2016	0
Prior	0
Doubtful | Commercial Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total	98,286
2020	0
2019	0
2018	33,460
2017	64,826
2016	0
Prior	0
Loss | Commercial Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	$ 0
Mezzanine loans | Commercial Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans | loan	1
Loan loss provision	$ 36,600