Fair Value Measurements and Disclosures - Estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financial assets:
Securities available-for-sale	$ 52,757	$ 50,428
Securities held-to-maturity	9,028	12,655
Mortgage loans held-for-investment	11,278	11,422
Interest rate lock commitments
Financial assets:
Derivative asset	283
Level 1 | Carrying amount
Financial assets:
Cash and cash equivalents	40,532	23,952
Level 1 | Fair value
Financial assets:
Cash and cash equivalents	40,532	23,952
Level 2 | Carrying amount
Financial assets:
Securities available-for-sale	52,757	50,428
Securities held-to-maturity	8,814	12,741
Mortgage loans held-for-sale	48,615	37,695
Mortgage loans held-for-investment	11,278	11,422
Financial liabilities:
Deposits	858,461	752,130
Short-term borrowings	128,466	114,300
Long-term debt	3,123	6,238
Subordinated debentures	9,176	9,239
Accrued interest payable	669	305
Level 2 | Carrying amount | Forward Commitments
Financial assets:
Derivative asset	30
Financial liabilities:
Derivatives	105	176
Level 2 | Carrying amount | Customer derivatives - Interest rate swaps
Financial assets:
Derivative asset	500	141
Financial liabilities:
Derivatives	568	161
Level 2 | Fair value
Financial assets:
Securities available-for-sale	52,757	50,428
Securities held-to-maturity	9,028	12,655
Mortgage loans held-for-sale	48,615	37,695
Mortgage loans held-for-investment	11,278	11,422
Financial liabilities:
Deposits	896,000	744,300
Short-term borrowings	128,467	114,300
Long-term debt	3,123	6,240
Subordinated debentures	9,792	9,396
Accrued interest payable	669	305
Level 2 | Fair value | Forward Commitments
Financial assets:
Derivative asset	30
Financial liabilities:
Derivatives	105	176
Level 2 | Fair value | Customer derivatives - Interest rate swaps
Financial assets:
Derivative asset	500	141
Financial liabilities:
Derivatives	568	161
Level 3 | Carrying amount
Financial assets:
Loans receivable, net	935,858	818,631
Restricted investment in bank stock	8,237	7,002
Mortgage servicing rights	314	232
SBA loan servicing rights	321
Accrued interest receivable	3,155	2,889
Level 3 | Carrying amount | Interest rate lock commitments
Financial assets:
Derivative asset	283	310
Financial liabilities:
Derivatives	81	40
Level 3 | Fair value
Financial assets:
Loans receivable, net	933,285	820,512
Restricted investment in bank stock	8,237	7,002
Mortgage servicing rights	314	213
SBA loan servicing rights	321
Accrued interest receivable	3,155	2,889
Level 3 | Fair value | Interest rate lock commitments
Financial assets:
Derivative asset	283	310
Financial liabilities:
Derivatives	$ 81	$ 40