FAIR VALUE MEASUREMENTS - Changes in Level 3 (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivative Asset (Liability)
Accounting standards update					us-gaap:AccountingStandardsUpdate201613Member
Commitments to lend
Changes in Level 3 assets that were measured at fair value on a recurring basis
Unrealized gain/(loss), net recognized in other non-interest income		$ 0	$ 0	$ 0
Unrealized gains (losses) relating to instruments still held at the end of the period	$ 1,498,000	7,084,000	1,498,000	7,084,000
Derivative Asset (Liability)
Beginning balance	1,149,000	9,005,000	2,628,000	3,927,000	$ 3,927,000
Unrealized gain/(loss), net recognized in other non-interest income		0	0	0
Transfers to held for sale loans	(1,775,000)	(21,836,000)	(17,007,000)	(45,097,000)
Ending balance	1,498,000	7,084,000	1,498,000	7,084,000	2,628,000
Forward Contracts
Changes in Level 3 assets that were measured at fair value on a recurring basis
Unrealized gain/(loss), net recognized in other non-interest income	(50,000)		397,000
Unrealized gains (losses) relating to instruments still held at the end of the period	397,000		397,000
Derivative Asset (Liability)
Beginning balance	447,000		0
Unrealized gain/(loss), net recognized in other non-interest income	(50,000)		397,000
Unrealized gain included in accumulated other comprehensive income	0
Ending balance	397,000		397,000		0
Trading Security
Changes in Level 3 assets that were measured at fair value on a recurring basis
Balance at the beginning of the period	9,519,000	11,210,000	10,769,000	11,212,000	11,212,000
Unrealized gain/(loss), net recognized in other non-interest income	190,000	109,000	(698,000)	454,000
Paydown of asset	(184,000)	(174,000)	(546,000)	(521,000)
Balance at the end of the period	9,525,000	11,145,000	9,525,000	11,145,000	10,769,000
Unrealized gains (losses) relating to instruments still held at the end of the period	682,000	1,576,000	682,000	1,576,000
Derivative Asset (Liability)
Unrealized gain/(loss), net recognized in other non-interest income	190,000	109,000	(698,000)	454,000
Available-for-sale Securities
Changes in Level 3 assets that were measured at fair value on a recurring basis
Balance at the beginning of the period	25,600,000	0	42,966,000	0	0
Maturity of AFS security			(17,000,000)
Unrealized gain (loss) included in accumulated other comprehensive income	225,000		(141,000)
Balance at the end of the period	25,825,000	0	25,825,000	0	42,966,000
Unrealized gains (losses) relating to instruments still held at the end of the period	(643)	0	(643)	0
Capitalized servicing rights
Changes in Level 3 assets that were measured at fair value on a recurring basis
Balance at the beginning of the period	4,828,000	11,206,000	12,299,000	11,485,000	11,485,000
Unrealized gain/(loss), net recognized in other non-interest income		0		0
Additions to servicing rights	0	6,588,000	(189,000)	9,423,000
Balance at the end of the period	3,855,000	16,413,000	3,855,000	16,413,000	12,299,000
Unrealized gains (losses) relating to instruments still held at the end of the period	0	0	0	0
Derivative Asset (Liability)
Unrealized gain/(loss), net recognized in other non-interest income		0		0
Loans Held for Investment
Changes in Level 3 assets that were measured at fair value on a recurring basis
Balance at the beginning of the period	3,140,000	0	0	0	0
Adoption of ASC 326			7,660,000
Unrealized gain/(loss), net recognized in other non-interest income	1,189,000		(2,523,000)
Paydown of asset	(1,555,000)		(2,363,000)
Balance at the end of the period	2,774,000	0	2,774,000	0	$ 0
Unrealized gains (losses) relating to instruments still held at the end of the period	0	0	0	0
Derivative Asset (Liability)
Unrealized gain/(loss), net recognized in other non-interest income	1,189,000		(2,523,000)
Discontinued Operations | Commitments to lend
Changes in Level 3 assets that were measured at fair value on a recurring basis
Unrealized gain/(loss), net recognized in discontinued operations	2,124,000	19,915,000	15,877,000	48,254,000
Derivative Asset (Liability)
Unrealized gain/(loss), net recognized in discontinued operations	2,124,000	19,915,000	15,877,000	48,254,000
Discontinued Operations | Trading Security
Changes in Level 3 assets that were measured at fair value on a recurring basis
Unrealized gain/(loss), net recognized in discontinued operations		0		0
Derivative Asset (Liability)
Unrealized gain/(loss), net recognized in discontinued operations		0		0
Discontinued Operations | Capitalized servicing rights
Changes in Level 3 assets that were measured at fair value on a recurring basis
Unrealized gain/(loss), net recognized in discontinued operations	(973,000)	(1,381,000)	(8,255,000)	(4,495,000)
Derivative Asset (Liability)
Unrealized gain/(loss), net recognized in discontinued operations	$ (973,000)	$ (1,381,000)	$ (8,255,000)	$ (4,495,000)