SECURITIES - Held to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized cost	$ 224,378	$ 563,529
Gross unrealized gains	89	4,901
Gross unrealized (losses)	(10,309)	(4,245)
Securities held to maturity	214,158	564,185
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
LESS THAN 12 MONTHS, Fair Value	119,644	315,838
LESS THAN 12 MONTHS, Unrealized (Losses)	(5,143)	(4,022)
OVER 12 MONTHS, Fair Value	88,411	10,295
OVER 12 MONTHS, Unrealized (Losses)	(5,166)	(223)
TOTAL, Fair Value	208,055	326,133
TOTAL, Unrealized (Losses)	(10,309)	(4,245)
AMORTIZED COST
Due in one year or less	2,395	1,483
Due after one year through five years	18,829	17,926
Due after five years through ten years	20,335	144,996
Due after ten years	174,601	285,435
Total	216,160	449,840
Mortgage-backed securities	8,218	113,689
Amortized cost	224,378	563,529
FAIR VALUE
Due in one year or less	2,390	1,480
Due after one year through five years	18,761	18,160
Due after five years through ten years	20,175	147,832
Due after ten years	164,986	284,257
Total	206,312	451,729
Mortgage-backed securities	7,846	112,456
Total held to maturity securities	214,158	564,185
Non-bank Qualified Obligations of States and Political Subdivisions [Member]
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized cost	212,329	430,593
Gross unrealized gains	73	4,744
Gross unrealized (losses)	(9,916)	(2,976)
Securities held to maturity	202,486	432,361
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
LESS THAN 12 MONTHS, Fair Value	118,237	202,018
LESS THAN 12 MONTHS, Unrealized (Losses)	(5,141)	(2,783)
OVER 12 MONTHS, Fair Value	79,222	6,206
OVER 12 MONTHS, Unrealized (Losses)	(4,775)	(193)
TOTAL, Fair Value	197,459	208,224
TOTAL, Unrealized (Losses)	(9,916)	(2,976)
AMORTIZED COST
Amortized cost	212,329	430,593
FAIR VALUE
Total held to maturity securities	202,486	432,361
Mortgage-backed Securities [Member]
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized cost	8,218	113,689
Gross unrealized gains	0	0
Gross unrealized (losses)	(372)	(1,233)
Securities held to maturity	7,846	112,456
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
LESS THAN 12 MONTHS, Fair Value	0	112,456
LESS THAN 12 MONTHS, Unrealized (Losses)	0	(1,233)
OVER 12 MONTHS, Fair Value	7,847	0
OVER 12 MONTHS, Unrealized (Losses)	(372)	0
TOTAL, Fair Value	7,847	112,456
TOTAL, Unrealized (Losses)	(372)	(1,233)
AMORTIZED COST
Amortized cost	8,218	113,689
FAIR VALUE
Total held to maturity securities	7,846	112,456
Obligations of States and Political Subdivisions [Member]
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized cost	3,831	19,247
Gross unrealized gains	16	157
Gross unrealized (losses)	(21)	(36)
Securities held to maturity	3,826	19,368
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
LESS THAN 12 MONTHS, Fair Value	1,407	1,364
LESS THAN 12 MONTHS, Unrealized (Losses)	(2)	(6)
OVER 12 MONTHS, Fair Value	1,342	4,089
OVER 12 MONTHS, Unrealized (Losses)	(19)	(30)
TOTAL, Fair Value	2,749	5,453
TOTAL, Unrealized (Losses)	(21)	(36)
AMORTIZED COST
Amortized cost	3,831	19,247
FAIR VALUE
Total held to maturity securities	$ 3,826	$ 19,368

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