INCOME TAXES (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Federal:
Current		$ (4,023,000)	$ 12,153,000	$ 4,410,000
Deferred		5,895,000	(5,040,000)	(440,000)
Federal income tax expense		1,872,000	7,113,000	3,970,000
State:
Current		2,611,000	4,366,000	1,422,000
Deferred		634,000	(1,246,000)	210,000
State tax expense		3,245,000	3,120,000	1,632,000
Income tax expense		5,117,000	10,233,000	5,602,000
Deferred tax assets:
Bad debts		3,224,000	2,832,000
Deferred compensation		3,495,000	1,548,000
Stock based compensation		3,758,000	3,436,000
AMT Credit		0	1,869,000
Intangibles		0	5,235,000
Net unrealized losses on securities available for sale		10,663,000	0
Valuation adjustments		6,991,000	0
General business credits		12,243,000	0
Accrued expenses		3,144,000	1,188,000
Other assets		1,629,000	1,579,000
Gross deferred tax assets		45,147,000	17,687,000
Deferred tax liabilities:
Premises and equipment		(347,000)	(1,713,000)
Intangibles		(4,231,000)	0
Net unrealized gains on securities available for sale		0	(4,934,000)
Deferred income		(2,070,000)	0
Leased assets		(17,985,000)	0
Leased assets		(1,777,000)	(1,939,000)
Gross deferred tax liabilities		(26,410,000)	(8,586,000)
Net deferred tax assets		18,737,000	9,101,000
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax expense at federal tax rate		14,082,000	19,303,000	13,588,000
Change in tax rate resulting from:
State income taxes net of federal benefits		2,461,000	2,014,000	933,000
Tax exempt income		(6,968,000)	(9,991,000)	(8,257,000)
Nondeductible acquisition costs		1,295,000	0	0
General business credits		(3,948,000)	0	0
Tax Reform		3,849,000	0	0
Amended Crestmark Bancorp historical tax return		(4,644,000)	0	0
Other, net		(1,010,000)	(1,093,000)	(662,000)
Income tax expense		$ 5,117,000	$ 10,233,000	$ 5,602,000
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax expense and rate (percent)		24.50%	35.00%	35.00%
State income taxes net of federal benefits (percent)		4.30%	3.70%	2.40%
Tax exempt income (percent)		(12.10%)	(18.10%)	(21.30%)
Nondeductible acquisition costs (percent)		2.30%	0.00%	0.00%
General business credits (percent)		(6.90%)	(0.00%)	(0.00%)
Tax Reform (percent)		6.70%	0.00%	0.00%
Amended Crestmark Bancorp historical tax return (percent)		(8.10%)	0.00%	0.00%
Other, net (percent)		(1.70%)	(2.00%)	(1.70%)
Total income tax expense (percent)		9.00%	18.60%	14.40%
Gross deferred tax on state net operating loss carryforwards		$ 2,000,000	$ 1,300,000
Operating loss carryforwards reserved		1,600,000
Additional bad debt deductions provided by federal income tax laws		6,700,000
Deferred tax liability, bad debt deductions		1,400,000	1,400,000
Change in Tax Rate, Income Tax Expense (Benefit)	$ 3,600,000
Tax credit, investment, amount		4,000,000	0	$ 0
Reconciliation for liabilities [Abstract]
Balance at beginning of year	$ 645,000	645,000	525,000
Additions for tax positions related to the current year		0	192,000
Additions for tax positions related to the prior years		0	31,000
Reductions for tax positions related to prior years		(211,000)	(103,000)
Balance at end of year		434,000	$ 645,000	$ 525,000
Unrecognized tax benefits that, if recognized, would impact the effective rate		384,000
Accrued interest related to unrecognized tax benefits		$ 68,000