Segment Reporting - Financial Statements Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2021 USD ($) segment	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)
Number of operating segments | segment			3
Net interest income (loss)	$ 14,780	$ 10,771	$ 28,519	$ 21,557
Provision for loan losses	287	1,705	955	2,210
Net interest income (loss) after provision	14,493	9,066	27,564	19,347
Net gains on sales of loans, SBA	3,239	1,229	4,506	1,990
Mortgage banking income	32,398	8,411	74,698	24,334
Noninterest income	38,973	11,133	85,156	29,365
Noninterest expense (income)	39,284	22,075	83,686	46,347
Income (loss) before taxes	14,182	(1,876)	29,034	2,365
Income tax expense	3,695	(774)	8,222	(136)
Segment profit (loss)	10,487	(1,102)	20,812	2,501
Non cash items:
Depreciation and amortization	584	352	1,132	761
Segment assets	1,750,609	1,368,252	1,750,609	1,368,252	$ 1,764,625
Core Banking Segment [Member]
Net interest income (loss)	11,422	9,335	22,587	18,644
Provision for loan losses	106	216	808	736
Net interest income (loss) after provision	11,316	9,119	21,779	17,908
Net gains on sales of loans, SBA		0
Mortgage banking income	2	3		4
Noninterest income	1,490	1,411	3,042	2,802
Noninterest expense (income)	9,224	6,809	17,510	14,002
Income (loss) before taxes	3,582	3,721	7,311	6,708
Income tax expense	633	801	1,322	1,317
Segment profit (loss)	2,949	2,920	5,989	5,391
Non cash items:
Depreciation and amortization	493	279	954	621
Segment assets	1,489,670	1,197,685	1,489,670	1,197,685
SBA Lending Segment [Member]
Net interest income (loss)	3,227	1,151	5,374	2,368
Provision for loan losses	181	1,489	147	1,474
Net interest income (loss) after provision	3,046	(338)	5,227	894
Net gains on sales of loans, SBA	3,239	1,229	4,506	1,990
Mortgage banking income		0
Noninterest income	3,407	1,209	4,792	2,138
Noninterest expense (income)	2,449	1,841	5,195	3,666
Income (loss) before taxes	4,004	(970)	4,824	(634)
Income tax expense	1,005	(124)	1,110	(81)
Segment profit (loss)	2,999	(846)	3,714	(553)
Non cash items:
Depreciation and amortization	12	14	23	27
Segment assets	257,566	106,296	257,566	106,296
Mortgage Banking Segment [Member]
Net interest income (loss)	439	585	1,170	1,142
Provision for loan losses		0
Net interest income (loss) after provision	439	585	1,170	1,142
Net gains on sales of loans, SBA		0
Mortgage banking income	32,396	8,408	74,698	24,330
Noninterest income	34,076	8,513	77,322	24,425
Noninterest expense (income)	27,844	13,514	61,388	28,852
Income (loss) before taxes	6,671	(4,416)	17,104	(3,285)
Income tax expense	2,183	(1,241)	6,035	(976)
Segment profit (loss)	4,488	(3,175)	11,069	(2,309)
Non cash items:
Depreciation and amortization	62	42	121	79
Segment assets	246,144	161,134	246,144	161,134
Other Segment [Member]
Net interest income (loss)	(308)	(300)	(612)	(597)
Provision for loan losses		0
Net interest income (loss) after provision	(308)	(300)	(612)	(597)
Net gains on sales of loans, SBA		0
Mortgage banking income		0
Noninterest income		0
Noninterest expense (income)	(233)	(89)	(407)	(173)
Income (loss) before taxes	(75)	(211)	(205)	(424)
Income tax expense	(126)	(210)	(245)	(396)
Segment profit (loss)	51	(1)	40	(28)
Non cash items:
Depreciation and amortization	17	17	34	34
Segment assets	$ (242,771)	$ (96,863)	$ (242,771)	$ (96,863)