FAIR VALUE, Recurring and Nonrecurring Fair Value Measurements (Details) - USD ($)	3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Instruments measured at fair value, Level 3, percentage of assets	15.40%	15.40%	19.00%
Assets, Fair Value Disclosure
Total debt securities	$ 644,638,000	$ 644,638,000		$ 581,837,000
Derivative contracts	51,275,000	51,275,000		42,086,000
Equity securities	54,524,000	54,524,000		28,344,000
Brokered certificates of deposit	32,257,000	32,257,000		30,803,000
Other	16,759,000	16,759,000		7,481,000
Total trading instruments	799,453,000	799,453,000		690,551,000
Available for sale securities	547,442,000	547,442,000		513,730,000
Derivative instruments associated with offsetting matched book positions	396,163,000	396,163,000		389,457,000
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	312,713,000	312,713,000		262,162,000
Derivative contracts	7,639,000	7,639,000		20,239,000
Equity securities	4,958,000	4,958,000		3,098,000
Other securities	100,000	100,000		2,494,000
Trading instruments sold but not yet purchased	325,410,000	325,410,000		287,993,000
Derivative instruments associated with offsetting matched book positions	396,163,000	396,163,000		389,457,000
Transfers of Financial Instruments into (out of) Level 1 and 2 [Abstract]
Fair value of financial instruments, level 1 to level 2 transfers	0	1,300,000		1,100,000
Fair value of financial instruments, level 2 to level 1 transfers	300,000	700,000		1,800,000
Adjustments to fair value of nonrecurring fair value measurements [Abstract]
Additional provision for loan losses due to fair value adjustment		2,000,000	$ 200,000
Other losses due to fair value adjustment		200,000	$ 100,000
Quoted prices in active markets for identical assets (Level 1)
Assets, Fair Value Disclosure
Total bank loans, net	0	0		0
Significant other observable inputs (Level 2)
Assets, Fair Value Disclosure
Total bank loans, net	93,926,000	93,926,000		105,199,000
Significant unobservable inputs (level 3)
Assets, Fair Value Disclosure
Total bank loans, net	14,149,555,000	14,149,555,000		12,799,065,000
Recurring
Assets, Fair Value Disclosure
Total debt securities	644,638,000	644,638,000		581,837,000
Netting adjustments	(96,630,000)	(96,630,000)		(90,621,000)
Equity securities	54,524,000	54,524,000		28,344,000
Brokered certificates of deposit	32,257,000	32,257,000		30,803,000
Other	16,759,000	16,759,000		7,481,000
Total trading instruments	799,453,000	799,453,000		690,551,000
Available for sale securities	547,442,000	547,442,000		513,730,000
Private equity investments	204,398,000	204,398,000		209,088,000
Other investments	294,098,000	294,098,000		248,751,000
Government and agency obligations	29,636,000	29,636,000		29,701,000
Total assets at fair value on a recurring basis	2,277,240,000	2,277,240,000		2,087,170,000
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	312,713,000	312,713,000		262,162,000
Netting adjustments	(128,002,000)	(128,002,000)		(88,881,000)
Equity securities	4,958,000	4,958,000		3,098,000
Other securities	100,000	100,000		2,494,000
Trading instruments sold but not yet purchased	325,410,000	325,410,000		287,993,000
Total liabilities at fair value on a recurring basis	742,644,000	742,644,000		685,053,000
Adjustments to fair value of nonrecurring fair value measurements [Abstract]
Other investments with obligations to perform under deferred compensation plan	103,000,000	103,000,000		106,000,000
Recurring | Municipal and provincial obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	4,000	4,000		18,313,000
Recurring | Corporate obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	48,860,000	48,860,000		33,184,000
Recurring | Government obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	260,727,000	260,727,000		205,658,000
Recurring | Agency MBS and CMOs
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	3,122,000	3,122,000		5,007,000
Recurring | Trade and other payables
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities	67,000	67,000		58,000
Trade and Other Liabilities, Fair Value Disclosure	21,071,000	21,071,000		7,603,000
Recurring | Municipal and provincial obligations
Assets, Fair Value Disclosure
Total debt securities	239,580,000	239,580,000		206,063,000
Recurring | Corporate obligations
Assets, Fair Value Disclosure
Total debt securities	137,061,000	137,061,000		95,317,000
Recurring | Government and agency obligations
Assets, Fair Value Disclosure
Total debt securities	133,487,000	133,487,000		115,947,000
Recurring | Agency MBS and CMOs
Assets, Fair Value Disclosure
Total debt securities	98,577,000	98,577,000		117,570,000
Available for sale securities	354,430,000	354,430,000		302,195,000
Recurring | Non-agency CMOs and ABS
Assets, Fair Value Disclosure
Total debt securities	35,933,000	35,933,000		46,940,000
Recurring | Non-agency CMOs
Assets, Fair Value Disclosure
Available for sale securities	63,694,000	63,694,000		71,369,000
Recurring | Other securities
Assets, Fair Value Disclosure
Available for sale securities	1,297,000	1,297,000		1,402,000
Recurring | ARS municipal obligations
Assets, Fair Value Disclosure
Available for sale securities	25,422,000	25,422,000		28,015,000
Recurring | ARS - preferred securities
Assets, Fair Value Disclosure
Available for sale securities	102,599,000	102,599,000		110,749,000
Recurring | Other assets
Assets, Fair Value Disclosure
Other assets	3,112,000	3,112,000		4,975,000
Total other assets	6,050,000	6,050,000		5,892,000
Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets, Fair Value Disclosure
Total debt securities	13,408,000	13,408,000		27,606,000
Equity securities	53,338,000	53,338,000		24,859,000
Brokered certificates of deposit	0	0		0
Other	534,000	534,000		679,000
Total trading instruments	67,280,000	67,280,000		53,144,000
Available for sale securities	1,297,000	1,297,000		1,402,000
Private equity investments	0	0		0
Other investments	271,885,000	271,885,000		230,839,000
Government and agency obligations	29,636,000	29,636,000		29,701,000
Total assets at fair value on a recurring basis	370,098,000	370,098,000		315,086,000
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	264,955,000	264,955,000		228,798,000
Equity securities	4,958,000	4,958,000		3,098,000
Other securities	0	0		0
Trading instruments sold but not yet purchased	269,913,000	269,913,000		231,896,000
Total liabilities at fair value on a recurring basis	269,913,000	269,913,000		231,896,000
Recurring | Quoted prices in active markets for identical assets (Level 1) | Municipal and provincial obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	4,000	4,000		17,966,000
Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	1,102,000	1,102,000		167,000
Recurring | Quoted prices in active markets for identical assets (Level 1) | Government obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	260,727,000	260,727,000		205,658,000
Recurring | Quoted prices in active markets for identical assets (Level 1) | Agency MBS and CMOs
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	3,122,000	3,122,000		5,007,000
Recurring | Quoted prices in active markets for identical assets (Level 1) | Trade and other payables
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities	0	0		0
Trade and Other Liabilities, Fair Value Disclosure	0	0		0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Municipal and provincial obligations
Assets, Fair Value Disclosure
Total debt securities	102,000	102,000		17,318,000
Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate obligations
Assets, Fair Value Disclosure
Total debt securities	4,976,000	4,976,000		2,254,000
Recurring | Quoted prices in active markets for identical assets (Level 1) | Government and agency obligations
Assets, Fair Value Disclosure
Total debt securities	7,897,000	7,897,000		7,781,000
Recurring | Quoted prices in active markets for identical assets (Level 1) | Agency MBS and CMOs
Assets, Fair Value Disclosure
Total debt securities	433,000	433,000		253,000
Available for sale securities	0	0		0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Non-agency CMOs and ABS
Assets, Fair Value Disclosure
Total debt securities	0	0		0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Non-agency CMOs
Assets, Fair Value Disclosure
Available for sale securities	0	0		0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Other securities
Assets, Fair Value Disclosure
Available for sale securities	1,297,000	1,297,000		1,402,000
Recurring | Quoted prices in active markets for identical assets (Level 1) | ARS municipal obligations
Assets, Fair Value Disclosure
Available for sale securities	0	0		0
Recurring | Quoted prices in active markets for identical assets (Level 1) | ARS - preferred securities
Assets, Fair Value Disclosure
Available for sale securities	0	0		0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Other assets
Assets, Fair Value Disclosure
Other assets	0	0		0
Total other assets	0	0		0
Recurring | Significant other observable inputs (Level 2)
Assets, Fair Value Disclosure
Total debt securities	631,222,000	631,222,000		554,066,000
Equity securities	1,186,000	1,186,000		3,485,000
Brokered certificates of deposit	32,257,000	32,257,000		30,803,000
Other	1,929,000	1,929,000		4,816,000
Total trading instruments	814,499,000	814,499,000		725,877,000
Available for sale securities	418,124,000	418,124,000		373,564,000
Private equity investments	0	0		0
Other investments	21,774,000	21,774,000		17,347,000
Government and agency obligations	0	0		0
Total assets at fair value on a recurring basis	1,653,498,000	1,653,498,000		1,507,162,000
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	47,758,000	47,758,000		33,364,000
Equity securities	0	0		0
Other securities	100,000	100,000		2,494,000
Trading instruments sold but not yet purchased	183,499,000	183,499,000		144,978,000
Total liabilities at fair value on a recurring basis	600,666,000	600,666,000		541,980,000
Recurring | Significant other observable inputs (Level 2) | Municipal and provincial obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	0	0		347,000
Recurring | Significant other observable inputs (Level 2) | Corporate obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	47,758,000	47,758,000		33,017,000
Recurring | Significant other observable inputs (Level 2) | Government obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	0	0		0
Recurring | Significant other observable inputs (Level 2) | Agency MBS and CMOs
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	0	0		0
Recurring | Significant other observable inputs (Level 2) | Trade and other payables
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities	0	0		0
Trade and Other Liabilities, Fair Value Disclosure	21,004,000	21,004,000		7,545,000
Recurring | Significant other observable inputs (Level 2) | Municipal and provincial obligations
Assets, Fair Value Disclosure
Total debt securities	239,478,000	239,478,000		188,745,000
Recurring | Significant other observable inputs (Level 2) | Corporate obligations
Assets, Fair Value Disclosure
Total debt securities	132,085,000	132,085,000		92,907,000
Recurring | Significant other observable inputs (Level 2) | Government and agency obligations
Assets, Fair Value Disclosure
Total debt securities	125,590,000	125,590,000		108,166,000
Recurring | Significant other observable inputs (Level 2) | Agency MBS and CMOs
Assets, Fair Value Disclosure
Total debt securities	98,144,000	98,144,000		117,317,000
Available for sale securities	354,430,000	354,430,000		302,195,000
Recurring | Significant other observable inputs (Level 2) | Non-agency CMOs and ABS
Assets, Fair Value Disclosure
Total debt securities	35,925,000	35,925,000		46,931,000
Recurring | Significant other observable inputs (Level 2) | Non-agency CMOs
Assets, Fair Value Disclosure
Available for sale securities	63,694,000	63,694,000		71,369,000
Recurring | Significant other observable inputs (Level 2) | Other securities
Assets, Fair Value Disclosure
Available for sale securities	0	0		0
Recurring | Significant other observable inputs (Level 2) | ARS municipal obligations
Assets, Fair Value Disclosure
Available for sale securities	0	0		0
Recurring | Significant other observable inputs (Level 2) | ARS - preferred securities
Assets, Fair Value Disclosure
Available for sale securities	0	0		0
Recurring | Significant other observable inputs (Level 2) | Other assets
Assets, Fair Value Disclosure
Other assets	0	0		0
Total other assets	2,938,000	2,938,000		917,000
Recurring | Significant unobservable inputs (level 3)
Assets, Fair Value Disclosure
Total debt securities	8,000	8,000		165,000
Equity securities	0	0		0
Brokered certificates of deposit	0	0		0
Other	14,296,000	14,296,000		1,986,000
Total trading instruments	14,304,000	14,304,000		2,151,000
Available for sale securities	128,021,000	128,021,000		138,764,000
Private equity investments	204,398,000	204,398,000		209,088,000
Other investments	439,000	439,000		565,000
Government and agency obligations	0	0		0
Total assets at fair value on a recurring basis	350,274,000	350,274,000		355,543,000
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	0	0		0
Equity securities	0	0		0
Other securities	0	0		0
Trading instruments sold but not yet purchased	0	0		0
Total liabilities at fair value on a recurring basis	67,000	67,000		58,000
Private Equity Investments [Abstract]
Portion of significant private equity investments included in noncontrolling interests	50,000,000	50,000,000		52,000,000
Portion of private equity investments owned by parent	$ 154,000,000	$ 154,000,000		$ 157,000,000
Weighted-average ownership percentage (in hundredths)	75.00%	75.00%		75.00%
Recurring | Significant unobservable inputs (level 3) | Municipal and provincial obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	$ 0	$ 0		$ 0
Recurring | Significant unobservable inputs (level 3) | Corporate obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	0	0		0
Recurring | Significant unobservable inputs (level 3) | Government obligations
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	0	0		0
Recurring | Significant unobservable inputs (level 3) | Agency MBS and CMOs
Liabilities, Fair Value Disclosure [Abstract]
Total debt securities	0	0		0
Recurring | Significant unobservable inputs (level 3) | Trade and other payables
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities	67,000	67,000		58,000
Trade and Other Liabilities, Fair Value Disclosure	67,000	67,000		58,000
Recurring | Significant unobservable inputs (level 3) | Municipal and provincial obligations
Assets, Fair Value Disclosure
Total debt securities	0	0		0
Recurring | Significant unobservable inputs (level 3) | Corporate obligations
Assets, Fair Value Disclosure
Total debt securities	0	0		156,000
Recurring | Significant unobservable inputs (level 3) | Government and agency obligations
Assets, Fair Value Disclosure
Total debt securities	0	0		0
Recurring | Significant unobservable inputs (level 3) | Agency MBS and CMOs
Assets, Fair Value Disclosure
Total debt securities	0	0		0
Available for sale securities	0	0		0
Recurring | Significant unobservable inputs (level 3) | Non-agency CMOs and ABS
Assets, Fair Value Disclosure
Total debt securities	8,000	8,000		9,000
Recurring | Significant unobservable inputs (level 3) | Non-agency CMOs
Assets, Fair Value Disclosure
Available for sale securities	0	0		0
Recurring | Significant unobservable inputs (level 3) | Other securities
Assets, Fair Value Disclosure
Available for sale securities	0	0		0
Recurring | Significant unobservable inputs (level 3) | ARS municipal obligations
Assets, Fair Value Disclosure
Available for sale securities	25,422,000	25,422,000		28,015,000
Recurring | Significant unobservable inputs (level 3) | ARS - preferred securities
Assets, Fair Value Disclosure
Available for sale securities	102,599,000	102,599,000		110,749,000
Recurring | Significant unobservable inputs (level 3) | Other assets
Assets, Fair Value Disclosure
Other assets	3,112,000	3,112,000		4,975,000
Total other assets	3,112,000	3,112,000		4,975,000
Nonrecurring
Assets, Fair Value Disclosure
Total bank loans, net	140,245,000	140,245,000		80,246,000
Other real estate owned (OREO)	238,000	238,000		671,000
Total assets at fair value on a nonrecurring basis	140,483,000	140,483,000		80,917,000
Nonrecurring | Impaired loans
Assets, Fair Value Disclosure
Total bank loans, net	61,948,000	61,948,000		65,912,000
Nonrecurring | Loans held for sale
Assets, Fair Value Disclosure
Total bank loans, net	78,297,000	78,297,000		14,334,000
Nonrecurring | Quoted prices in active markets for identical assets (Level 1)
Assets, Fair Value Disclosure
Total bank loans, net	0	0		0
Other real estate owned (OREO)	0	0		0
Total assets at fair value on a nonrecurring basis	0	0		0
Nonrecurring | Quoted prices in active markets for identical assets (Level 1) | Impaired loans
Assets, Fair Value Disclosure
Total bank loans, net	0	0		0
Nonrecurring | Quoted prices in active markets for identical assets (Level 1) | Loans held for sale
Assets, Fair Value Disclosure
Total bank loans, net	0	0		0
Nonrecurring | Significant other observable inputs (Level 2)
Assets, Fair Value Disclosure
Total bank loans, net	104,525,000	104,525,000		42,416,000
Other real estate owned (OREO)	238,000	238,000		671,000
Total assets at fair value on a nonrecurring basis	104,763,000	104,763,000		43,087,000
Nonrecurring | Significant other observable inputs (Level 2) | Impaired loans
Assets, Fair Value Disclosure
Total bank loans, net	26,228,000	26,228,000		28,082,000
Nonrecurring | Significant other observable inputs (Level 2) | Loans held for sale
Assets, Fair Value Disclosure
Total bank loans, net	78,297,000	78,297,000		14,334,000
Nonrecurring | Significant unobservable inputs (level 3)
Assets, Fair Value Disclosure
Total bank loans, net	35,720,000	35,720,000		37,830,000
Other real estate owned (OREO)	0	0		0
Total assets at fair value on a nonrecurring basis	35,720,000	35,720,000		37,830,000
Nonrecurring | Significant unobservable inputs (level 3) | Impaired loans
Assets, Fair Value Disclosure
Total bank loans, net	35,720,000	35,720,000		37,830,000
Nonrecurring | Significant unobservable inputs (level 3) | Loans held for sale
Assets, Fair Value Disclosure
Total bank loans, net	0	0		0
Interest rate contract | Recurring
Assets, Fair Value Disclosure
Netting adjustments	(96,630,000)	(96,630,000)		(90,621,000)
Derivative contracts	51,275,000	51,275,000		42,086,000
Derivative instruments associated with offsetting matched book positions	396,163,000	396,163,000		389,457,000
Liabilities, Fair Value Disclosure [Abstract]
Netting adjustments	(128,002,000)	(128,002,000)		(88,881,000)
Derivative contracts	7,639,000	7,639,000		20,239,000
Derivative instruments associated with offsetting matched book positions	396,163,000	396,163,000		389,457,000
Interest rate contract | Recurring | Trade and other payables
Liabilities, Fair Value Disclosure [Abstract]
Derivative contracts	21,004,000	21,004,000		7,545,000
Interest rate contract | Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets, Fair Value Disclosure
Derivative contracts	0	0		0
Derivative instruments associated with offsetting matched book positions	0	0		0
Liabilities, Fair Value Disclosure [Abstract]
Derivative contracts	0	0		0
Derivative instruments associated with offsetting matched book positions	0	0		0
Interest rate contract | Recurring | Quoted prices in active markets for identical assets (Level 1) | Trade and other payables
Liabilities, Fair Value Disclosure [Abstract]
Derivative contracts	0	0		0
Interest rate contract | Recurring | Significant other observable inputs (Level 2)
Assets, Fair Value Disclosure
Derivative contracts	147,905,000	147,905,000		132,707,000
Derivative instruments associated with offsetting matched book positions	396,163,000	396,163,000		389,457,000
Liabilities, Fair Value Disclosure [Abstract]
Derivative contracts	135,641,000	135,641,000		109,120,000
Derivative instruments associated with offsetting matched book positions	396,163,000	396,163,000		389,457,000
Interest rate contract | Recurring | Significant other observable inputs (Level 2) | Trade and other payables
Liabilities, Fair Value Disclosure [Abstract]
Derivative contracts	21,004,000	21,004,000		7,545,000
Interest rate contract | Recurring | Significant unobservable inputs (level 3)
Assets, Fair Value Disclosure
Derivative contracts	0	0		0
Derivative instruments associated with offsetting matched book positions	0	0		0
Liabilities, Fair Value Disclosure [Abstract]
Derivative contracts	0	0		0
Derivative instruments associated with offsetting matched book positions	0	0		0
Interest rate contract | Recurring | Significant unobservable inputs (level 3) | Trade and other payables
Liabilities, Fair Value Disclosure [Abstract]
Derivative contracts	0	0		0
Forward foreign exchange contracts | Recurring | Other assets
Assets, Fair Value Disclosure
Derivative contracts	2,938,000	2,938,000		917,000
Forward foreign exchange contracts | Recurring | Quoted prices in active markets for identical assets (Level 1) | Other assets
Assets, Fair Value Disclosure
Derivative contracts	0	0		0
Forward foreign exchange contracts | Recurring | Significant other observable inputs (Level 2) | Other assets
Assets, Fair Value Disclosure
Derivative contracts	2,938,000	2,938,000		917,000
Forward foreign exchange contracts | Recurring | Significant unobservable inputs (level 3) | Other assets
Assets, Fair Value Disclosure
Derivative contracts	$ 0	$ 0		$ 0