Loans Receivable and Allowance For Loan Losses - Aging Analysis of Past Due Loans) (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan	Mar. 31, 2019 USD ($)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 5,293	$ 4,159
Current	1,406,581	1,347,734
Total loans receivable	1,411,874	1,351,893	$ 1,297,070
REAL ESTATE LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	862,676	824,040	833,415
REAL ESTATE LOANS. | REAL ESTATE LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	862,676	824,040
Total real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,028	2,985
Current	858,648	821,055
Total loans receivable	862,676	824,040
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	220,509	210,749
Total loans receivable	220,509	210,749
Commercial | REAL ESTATE LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	220,509	210,749
Construction and development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	533
Current	168,658	179,121
Total loans receivable	168,658	179,654
Construction and development | REAL ESTATE LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	168,658	179,654
Home equity.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	713	294
Current	36,790	37,873
Total loans receivable	37,503	38,167
Home equity. | REAL ESTATE LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	37,503	38,167
One-to-four-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,315	2,158
Current	302,121	259,381
Total loans receivable	305,436	261,539
One-to-four-family | REAL ESTATE LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	305,436	261,539
Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	130,570	133,931
Total loans receivable	130,570	133,931
Multi-family | REAL ESTATE LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	130,570	133,931
CONSUMER LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,265	1,174
Current	333,830	325,036
Total loans receivable	335,095	326,210	284,416
CONSUMER LOANS. | CONSUMER LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	335,095	326,210
Indirect home improvement
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,091	1,066
Current	260,475	253,625
Total loans receivable	261,566	254,691
Indirect home improvement | CONSUMER LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	261,566	254,691
Marine
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	138	15
Current	69,335	67,164
Total loans receivable	69,473	67,179
Marine | CONSUMER LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	69,473	67,179
Other consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	36	93
Current	4,020	4,247
Total loans receivable	4,056	4,340
Other consumer loans | CONSUMER LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	4,056	4,340
COMMERCIAL BUSINESS LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	214,103	201,643
Total loans receivable	214,103	201,643	$ 179,239
COMMERCIAL BUSINESS LOANS. | COMMERCIAL BUSINESS LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	214,103	201,643
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	149,086	140,531
Total loans receivable	149,086	140,531
Commercial and industrial | COMMERCIAL BUSINESS LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	149,086	140,531
Warehouse lending
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	65,017	61,112
Total loans receivable	65,017	61,112
Warehouse lending | COMMERCIAL BUSINESS LOANS
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	65,017	61,112
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,097	2,314
30-59 Days Past Due | Total real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,407	1,536
30-59 Days Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
30-59 Days Past Due | Construction and development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	533
30-59 Days Past Due | Home equity.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	204	109
30-59 Days Past Due | One-to-four-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,203	894
30-59 Days Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
30-59 Days Past Due | CONSUMER LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	690	778
30-59 Days Past Due | Indirect home improvement
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	654	692
30-59 Days Past Due | Marine
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14	15
30-59 Days Past Due | Other consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	22	71
30-59 Days Past Due | COMMERCIAL BUSINESS LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
30-59 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
30-59 Days Past Due | Warehouse lending
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	567	343
60-89 Days Past Due | Total real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	289	114
60-89 Days Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due | Construction and development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due | Home equity.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	289	0
60-89 Days Past Due | One-to-four-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	114
60-89 Days Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due | CONSUMER LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	278	229
60-89 Days Past Due | Indirect home improvement
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	266	227
60-89 Days Past Due | Marine
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due | Other consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12	2
60-89 Days Past Due | COMMERCIAL BUSINESS LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due | Warehouse lending
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,629	$ 1,502
Number Of Loans Accruing Interest | loan	0	0
90 Days or More Past Due | Total real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,332	$ 1,335
90 Days or More Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
90 Days or More Past Due | Construction and development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
90 Days or More Past Due | Home equity.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	220	185
90 Days or More Past Due | One-to-four-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,112	1,150
90 Days or More Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
90 Days or More Past Due | CONSUMER LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	297	167
90 Days or More Past Due | Indirect home improvement
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	171	147
90 Days or More Past Due | Marine
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	124	0
90 Days or More Past Due | Other consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2	20
90 Days or More Past Due | COMMERCIAL BUSINESS LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
90 Days or More Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
90 Days or More Past Due | Warehouse lending
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Non-Accrual
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,192	3,033
Non-Accrual | Total real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,528	2,540
Non-Accrual | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,083	1,086
Non-Accrual | Construction and development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Non-Accrual | Home equity.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	220	190
Non-Accrual | One-to-four-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,225	1,264
Non-Accrual | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Non-Accrual | CONSUMER LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	664	493
Non-Accrual | Indirect home improvement
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	533	468
Non-Accrual | Marine
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	124	0
Non-Accrual | Other consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7	25
Non-Accrual | COMMERCIAL BUSINESS LOANS.
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Non-Accrual | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Non-Accrual | Warehouse lending
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 0