SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)		Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	3
Segment data [Abstract]
Total interest and dividend income	$ 30,857	$ 22,575
Interest expense	4,661	2,742
Net interest income (expense)	26,196	19,833
Net excess tax benefit from stock-based compensation	1,068	843	[1]
Non-interest income	29,268	19,349
Non-interest expense	44,042	36,753
Income before income tax expense	10,354	1,586
Goodwill	98,723	98,898		$ 98,723	$ 36,928
Total assets	5,417,963	4,213,329		5,228,332
Total deposits	3,513,645	3,663,137		$ 3,223,424
Payments [Member]
Segment data [Abstract]
Total interest and dividend income	4,669	2,912
Interest expense	0	0
Net interest income (expense)	4,669	2,912
Net excess tax benefit from stock-based compensation	1,017	331
Non-interest income	28,101	19,024
Non-interest expense	26,934	22,080
Income before income tax expense	4,819	(475)
Goodwill	87,145	87,320
Total assets	380,442	239,804
Total deposits	2,768,736	2,435,530
Banking [Member]
Segment data [Abstract]
Total interest and dividend income	16,478	10,754
Interest expense	881	544
Net interest income (expense)	15,597	10,210
Net excess tax benefit from stock-based compensation	51	512
Non-interest income	1,485	1,072
Non-interest expense	6,568	5,845
Income before income tax expense	10,463	4,925
Goodwill	11,578	11,578
Total assets	1,478,693	1,118,429
Total deposits	236,494	225,182
Corporate and Other [Member]
Segment data [Abstract]
Total interest and dividend income	9,710	8,909
Interest expense	3,780	2,198
Net interest income (expense)	5,930	6,711
Net excess tax benefit from stock-based compensation	0	0
Non-interest income	(318)	(747)
Non-interest expense	10,540	8,828
Income before income tax expense	(4,928)	(2,864)
Goodwill	0	0
Total assets	3,558,828	2,855,096
Total deposits	$ 508,415	$ 1,002,425

[1] See Note 1. Basis of Presentation for further discussion on the current presentation.