FAIR VALUE - Summary of carrying amounts and estimated fair values for financial instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	$ 191,676	$ 78,638	$ 92,769	$ 73,357
Fair Value	47,018	58,903
Loans, net	1,412,086	990,132
Mortgage loans held for sale	69,604	48,312
Accrued interest receivable	5,108	3,048
Other assets	23,141	16,544
Liabilities
Deposits	1,406,932	1,086,784
FHLB Topeka Borrowings - fixed rate	222,313	10,000
Subordinated notes	14,444	6,560
Accrued interest payable	205	299
Carrying Amount
Assets
Cash and cash equivalents	191,676	78,638
Fair Value	47,018	58,903
Loans, net	1,412,086	990,132
Mortgage loans held for sale	69,604	48,312
Accrued interest receivable	5,108	3,048
Equity securities	732
Guarantee asset	222
Other assets		713
Liabilities
Deposits	1,406,932	1,086,784
FHLB Topeka Borrowings - fixed rate	18,000	10,000
Federal Reserve Borrowings - fixed rate	204,313
Accrued interest payable	205	299
Guarantee liability	191
Subordinated notes - fixed-to-floating rate | Carrying Amount
Liabilities
Subordinated notes	14,444	6,560
Level 1 | Estimated Fair Value
Assets
Cash and cash equivalents	191,676	78,638
Fair Value	257	254
Equity securities	732
Other assets		713
Level 2 | Estimated Fair Value
Assets
Fair Value	46,761	58,649
Mortgage loans held for sale	69,604	48,312
Accrued interest receivable	5,108	3,048
Liabilities
Deposits	1,408,813	1,089,261
FHLB Topeka Borrowings - fixed rate	18,011	10,003
Federal Reserve Borrowings - fixed rate	204,313
Accrued interest payable	205	299
Level 3 | Estimated Fair Value
Assets
Loans, net	1,412,463	974,142
Guarantee asset	222
Liabilities
Guarantee liability	191
Level 3 | Subordinated notes - fixed-to-floating rate | Estimated Fair Value
Liabilities
Subordinated notes	$ 14,799	$ 6,004