DERIVATIVE INSTRUMENTS - Schedule of Derivatives Outstanding (Details) - USD ($)		6 Months Ended	12 Months Ended
		Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional		$ 344,171,000	$ 578,971,000
Fair value, asset	[1]	536,000	0
Fair value, liability	[1]	0	975,000
1 Month LIBOR
Derivative [Line Items]
Notional		69,571,000	69,571,000
Fair value, asset		0	0
Fair value, liability		$ 0	$ 0
Remaining maturity		10 months 9 days	1 year 4 months 6 days
5-year Swap
Derivative [Line Items]
Notional		$ 95,800,000	$ 274,900,000
Fair value, asset		187,000	0
Fair value, liability		$ 0	$ 526,000
Remaining maturity		3 months	3 months
10-year Swap
Derivative [Line Items]
Notional		$ 175,900,000	$ 227,700,000
Fair value, asset		343,000	0
Fair value, liability		$ 0	$ 436,000
Remaining maturity		3 months	3 months
5-year U.S. Treasury Note
Derivative [Line Items]
Notional		$ 2,900,000	$ 6,800,000
Fair value, asset		6,000	0
Fair value, liability		$ 0	$ 13,000
Remaining maturity		3 months	3 months
Futures
Derivative [Line Items]
Notional		$ 274,600,000	$ 509,400,000
Fair value, asset		536,000	0
Fair value, liability		$ 0	$ 975,000

[1] Includes amounts relating to consolidated variable interest entities. See Note 3.