SECURITIES - Held to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Sep. 30, 2015
Held-to-maturity Securities [Abstract]
Amortized cost	$ 604,589	$ 345,744
Gross unrealized gains	13,583	2,182
Gross unrealized (losses)	(22)	(1,079)
Fair value	618,150	346,847
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
LESS THAN 12 MONTHS, Fair Value	0	89,700
LESS THAN 12 MONTHS, Unrealized (Losses)	0	(442)
OVER 12 MONTHS, Fair Value	2,266	72,695
OVER 12 MONTHS, Unrealized (Losses)	(22)	(637)
TOTAL, Fair Value	2,266	162,395
TOTAL, Unrealized (Losses)	(22)	(1,079)
AMORTIZED COST [Abstract]
Due in one year or less	231	95
Due after one year through five years	11,586	8,411
Due after five years through ten years	147,795	140,145
Due after ten years	305,839	130,516
Total	465,451	279,167
Mortgage-backed securities	139,138	66,577
Amortized cost	604,589	345,744
FAIR VALUE [Abstract]
Due in one year or less	231	96
Due after one year through five years	11,810	8,430
Due after five years through ten years	153,986	140,505
Due after ten years	312,365	131,712
Total	478,392	280,743
Mortgage-backed securities	139,758	66,104
Total held to maturity securities	618,150	346,847
Non-bank Qualified Obligations of States and Political Subdivisions [Member]
Held-to-maturity Securities [Abstract]
Amortized cost	444,807	259,627
Gross unrealized gains	12,529	2,122
Gross unrealized (losses)	0	(419)
Fair value	457,336	261,330
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
LESS THAN 12 MONTHS, Fair Value		78,663
LESS THAN 12 MONTHS, Unrealized (Losses)		(365)
OVER 12 MONTHS, Fair Value		4,136
OVER 12 MONTHS, Unrealized (Losses)		(54)
TOTAL, Fair Value		82,799
TOTAL, Unrealized (Losses)		(419)
AMORTIZED COST [Abstract]
Amortized cost	444,807	259,627
FAIR VALUE [Abstract]
Total held to maturity securities	457,336	261,330
Mortgage-backed Securities [Member]
Held-to-maturity Securities [Abstract]
Amortized cost	139,138	66,577
Gross unrealized gains	620	0
Gross unrealized (losses)	0	(473)
Fair value	139,758	66,104
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
LESS THAN 12 MONTHS, Fair Value		5,509
LESS THAN 12 MONTHS, Unrealized (Losses)		(43)
OVER 12 MONTHS, Fair Value		60,595
OVER 12 MONTHS, Unrealized (Losses)		(430)
TOTAL, Fair Value		66,104
TOTAL, Unrealized (Losses)		(473)
AMORTIZED COST [Abstract]
Amortized cost	139,138	66,577
FAIR VALUE [Abstract]
Total held to maturity securities	139,758	66,104
Obligations of States and Political Subdivisions [Member]
Held-to-maturity Securities [Abstract]
Amortized cost	20,644	19,540
Gross unrealized gains	434	60
Gross unrealized (losses)	(22)	(187)
Fair value	21,056	19,413
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
LESS THAN 12 MONTHS, Fair Value	0	5,528
LESS THAN 12 MONTHS, Unrealized (Losses)	0	(34)
OVER 12 MONTHS, Fair Value	2,266	7,964
OVER 12 MONTHS, Unrealized (Losses)	(22)	(153)
TOTAL, Fair Value	2,266	13,492
TOTAL, Unrealized (Losses)	(22)	(187)
AMORTIZED COST [Abstract]
Amortized cost	20,644	19,540
FAIR VALUE [Abstract]
Total held to maturity securities	$ 21,056	$ 19,413

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for twelve months or longer.

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Fair value of held-to-maturity debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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