Loans - Allowance for loan losses and the recorded investment (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Ending allowance balance attributable to loans:
Individually evaluated for impairment	$ 490	$ 595
Collectively evaluated for impairment	28,444	27,736
Acquired with deteriorated credit quality	0	0
Total ending allowance balance	28,934	28,331
Loans:
Loans individually evaluated for impairment	41,205	45,940
Loans collectively evaluated for impairment	2,590,486	2,500,222
Loans acquired with deteriorated credit quality	2,067	2,331
Total ending loans balance	2,633,758	2,548,493
One to Four Family Residential Real Estate [Member]
Ending allowance balance attributable to loans:
Individually evaluated for impairment	196	175
Collectively evaluated for impairment	2,597	2,706
Acquired with deteriorated credit quality	0	0
Total ending allowance balance	2,793	2,881
Loans:
Loans individually evaluated for impairment	7,230	6,774
Loans collectively evaluated for impairment	314,359	315,385
Loans acquired with deteriorated credit quality	1,003	1,012
Total ending loans balance	322,592	323,171
Multi Family Residential Real Estate [Member]
Ending allowance balance attributable to loans:
Individually evaluated for impairment	2	3
Collectively evaluated for impairment	3,100	3,098
Acquired with deteriorated credit quality	0	0
Total ending allowance balance	3,102	3,101
Loans:
Loans individually evaluated for impairment	179	1,347
Loans collectively evaluated for impairment	281,595	277,105
Loans acquired with deteriorated credit quality	293	296
Total ending loans balance	282,067	278,748
Commercial Real Estate [Member]
Ending allowance balance attributable to loans:
Individually evaluated for impairment	65	95
Collectively evaluated for impairment	12,084	11,946
Acquired with deteriorated credit quality	0	0
Total ending allowance balance	12,149	12,041
Loans:
Loans individually evaluated for impairment	24,144	26,334
Loans collectively evaluated for impairment	1,108,728	1,102,355
Loans acquired with deteriorated credit quality	652	846
Total ending loans balance	1,133,524	1,129,535
Construction Loans [Member]
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	887	682
Acquired with deteriorated credit quality	0	0
Total ending allowance balance	887	682
Loans:
Loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	200,767	142,096
Loans acquired with deteriorated credit quality	0	0
Total ending loans balance	200,767	142,096
Commercial [Member]
Ending allowance balance attributable to loans:
Individually evaluated for impairment	161	79
Collectively evaluated for impairment	7,727	7,202
Acquired with deteriorated credit quality	0	0
Total ending allowance balance	7,888	7,281
Loans:
Loans individually evaluated for impairment	8,749	10,477
Loans collectively evaluated for impairment	523,640	500,730
Loans acquired with deteriorated credit quality	119	177
Total ending loans balance	532,508	511,384
Home Equity and Home Improvement [Member]
Ending allowance balance attributable to loans:
Individually evaluated for impairment	66	242
Collectively evaluated for impairment	1,697	1,784
Acquired with deteriorated credit quality	0	0
Total ending allowance balance	1,763	2,026
Loans:
Loans individually evaluated for impairment	881	963
Loans collectively evaluated for impairment	125,921	128,065
Loans acquired with deteriorated credit quality	0	0
Total ending loans balance	126,802	129,028
Consumer Finance [Member]
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	1
Collectively evaluated for impairment	352	318
Acquired with deteriorated credit quality	0	0
Total ending allowance balance	352	319
Loans:
Loans individually evaluated for impairment	22	45
Loans collectively evaluated for impairment	35,476	34,486
Loans acquired with deteriorated credit quality	0	0
Total ending loans balance	$ 35,498	$ 34,531