SEGMENT REPORTING (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($) segment	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Segment data [Abstract]
Net interest income	$ 71,350	$ 27,405	$ 131,622	$ 53,601
Provision for loan and lease losses	33,318	18,343	42,417	19,411
Noninterest income	105,025	97,419	142,776	126,687
Noninterest expense	110,254	68,497	184,549	112,539
Income (loss) before income tax expense (benefit)	32,803	37,984	47,432	48,338
Total assets	6,050,042	4,301,693	6,050,042	4,301,693	$ 5,835,067
Goodwill	307,464	98,723	307,464	98,723	303,270	$ 98,723
Total deposits	4,970,307	3,340,497	4,970,307	3,340,497	4,430,987
Meta Payment Systems
Segment data [Abstract]
Net interest income	13,607	4,933	23,007	9,602
Provision for loan and lease losses	22,474	18,129	23,969	19,146
Noninterest income	89,752	95,673	112,578	123,774
Noninterest expense	32,178	44,841	53,539	71,796
Income (loss) before income tax expense (benefit)	48,707	37,636	58,077	42,434
Total assets	245,872	243,140	245,872	243,140
Goodwill	87,145	87,145	87,145	87,145	87,145	87,145
Total deposits	3,107,264	2,882,441	3,107,264	2,882,441
Banking
Segment data [Abstract]
Net interest income	56,271	16,120	108,063	31,717
Provision for loan and lease losses	10,844	214	18,448	265
Noninterest income	13,948	1,241	28,217	2,726
Noninterest expense	42,522	6,984	76,365	13,552
Income (loss) before income tax expense (benefit)	16,853	10,163	41,467	20,626
Total assets	3,884,673	1,510,939	3,884,673	1,510,939
Goodwill	220,319	11,578	220,319	11,578	216,125	11,578
Total deposits	482,033	244,149	482,033	244,149
Corporate Services/Other
Segment data [Abstract]
Net interest income	1,472	6,352	552	12,282
Provision for loan and lease losses	0	0	0	0
Noninterest income	1,325	505	1,981	187
Noninterest expense	35,554	16,672	54,645	27,191
Income (loss) before income tax expense (benefit)	(32,757)	(9,815)	(52,112)	(14,722)
Total assets	1,919,497	2,547,614	1,919,497	2,547,614
Goodwill	0	0	0	0	$ 0	$ 0
Total deposits	$ 1,381,010	$ 213,907	$ 1,381,010	$ 213,907