SHORT TERM AND LONG TERM DEBT SHORT TERM AND LONG TERM DEBT - Short Term Debt (Details)	12 Months Ended
	Sep. 30, 2017 USD ($) Lease	Sep. 30, 2016 USD ($)
Short-term Debt [Line Items]
Short-term debt	$ 1,404,534,000	$ 1,095,118,000
Fixed rate of FHLB advances	1.27%
Pledged securities against specific FHLB advances, fair value	$ 1,070,000,000	824,500,000
Qualified mortgage loans pledged as collateral	$ 628,000,000	501,000,000
Number of capital leases | Lease	3
Number of equipment leases | Lease	2
Number of property leases | Lease	1
Leases, current	$ 79,507
Securities sold under agreements to repurchase, total	2,500,000	3,000,000
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Abstract]
Highest month-end balance	3,782,000	3,468,000
Average balance	$ 2,225,000	$ 2,179,000
Weighted average interest rate for the year	0.98%	0.60%
Weighted average interest rate at year end	1.59%	0.61%
Securities pledged as collateral for securities sold under agreement to repurchase, fair value	$ 9,300,000	$ 9,200,000
Overnight federal funds purchased [Member]
Short-term Debt [Line Items]
Short-term debt	987,000,000	992,000,000
Short-term FHLB advances [Member]
Short-term Debt [Line Items]
Short-term debt	415,000,000	100,000,000
Short-term capital lease [Member]
Short-term Debt [Line Items]
Short-term debt	62,000	79,000
Repurchase agreements [Member]
Short-term Debt [Line Items]
Short-term debt	$ 2,472,000	$ 3,039,000