Fair Value Measurements and Disclosures - Estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Securities available-for-sale	$ 50,440	$ 50,428
Securities held-to-maturity	12,814	12,655
Mortgage loans held-for-investment	12,751	11,422
Interest rate lock commitments
Financial assets:
Derivative asset	329
Level 1 | Carrying amount
Financial assets:
Cash and cash equivalents	38,940	23,952
Level 1 | Fair value
Financial assets:
Cash and cash equivalents	38,940	23,952
Level 2 | Carrying amount
Financial assets:
Securities available-for-sale	50,440	50,428
Securities held-to-maturity	12,712	12,741
Mortgage loans held-for-sale	29,612	37,695
Mortgage loans held-for-investment	12,751	11,422
Financial liabilities:
Deposits	810,713	752,130
Short-term borrowings	82,233	114,300
Long-term debt	6,031	6,238
Subordinated debentures	9,239	9,239
Accrued interest payable	434	305
Level 2 | Carrying amount | Forward Commitments
Financial liabilities:
Derivatives	170	176
Level 2 | Carrying amount | Customer derivatives - Interest rate swaps
Financial assets:
Derivative asset	229	141
Financial liabilities:
Derivatives	260	161
Level 2 | Fair value
Financial assets:
Securities available-for-sale	50,440	50,428
Securities held-to-maturity	12,814	12,655
Mortgage loans held-for-sale	29,612	37,695
Mortgage loans held-for-investment	12,751	11,422
Financial liabilities:
Deposits	817,200	744,300
Short-term borrowings	82,233	114,300
Long-term debt	6,034	6,240
Subordinated debentures	9,396	9,396
Accrued interest payable	434	305
Level 2 | Fair value | Forward Commitments
Financial liabilities:
Derivatives	170	176
Level 2 | Fair value | Customer derivatives - Interest rate swaps
Financial assets:
Derivative asset	229	141
Financial liabilities:
Derivatives	260	161
Level 3 | Carrying amount
Financial assets:
Loans receivable, net	841,245	818,631
Restricted investment in bank stock	6,179	7,002
Accrued interest receivable	3,001	2,889
Level 3 | Carrying amount | Interest rate lock commitments
Financial assets:
Derivative asset	330	310
Financial liabilities:
Derivatives	41	40
Level 3 | Fair value
Financial assets:
Loans receivable, net	849,409	820,512
Restricted investment in bank stock	6,179	7,002
Accrued interest receivable	3,001	2,889
Level 3 | Fair value | Interest rate lock commitments
Financial assets:
Derivative asset	330	310
Financial liabilities:
Derivatives	$ 41	$ 40