BANK LOANS, NET, Allowance for Loan Losses, Loans Individually and Collectively Evaluated for Impairment (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Allowance for loan losses:
Total allowance for loan losses	$ 172,257	$ 147,574	$ 136,501	$ 147,541
Recorded investment [Abstract]
Total loans held for investment	13,073,183	11,103,418	8,891,346	8,049,236	$ 6,636,839
Reserve for unfunded lending commitments [Abstract]
Reserve for unfunded lending commitments	9,700	10,000
C&I loans
Recorded investment [Abstract]
Total loans held for investment	6,928,018	6,422,347
CRE construction
Recorded investment [Abstract]
Total loans held for investment	162,356	94,195
CRE
Recorded investment [Abstract]
Total loans held for investment	2,054,154	1,689,163
Tax-exempt
Recorded investment [Abstract]
Total loans held for investment	484,537	122,218
SBL
Recorded investment [Abstract]
Total loans held for investment	1,481,504	1,023,748
Loans held for investment
Allowance for loan losses:
Individually evaluated for impairment	5,178	6,301
Collectively evaluated for impairment	167,079	141,273
Total allowance for loan losses	172,257	147,574
Recorded investment [Abstract]
Individually evaluated for impairment	78,101	96,628
Collectively evaluated for impairment	12,995,082	11,006,790
Total loans held for investment	13,073,183	11,103,418
Loans held for investment | C&I loans
Allowance for loan losses:
Individually evaluated for impairment	1,132	1,289
Collectively evaluated for impairment	116,491	101,890
Total allowance for loan losses	117,623	103,179	95,994	92,409
Recorded investment [Abstract]
Individually evaluated for impairment	10,599	11,959
Collectively evaluated for impairment	6,917,419	6,410,388
Total loans held for investment	6,928,018	6,422,347
Loans held for investment | CRE construction
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	2,707	1,594
Total allowance for loan losses	2,707	1,594	1,000	739
Recorded investment [Abstract]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	162,356	94,195
Total loans held for investment	162,356	94,195
Loans held for investment | CRE
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	30,486	25,022
Total allowance for loan losses	30,486	25,022	19,266	27,546
Recorded investment [Abstract]
Individually evaluated for impairment	4,796	18,876
Collectively evaluated for impairment	2,049,358	1,670,287
Total loans held for investment	2,054,154	1,689,163
Loans held for investment | Tax-exempt
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	5,949	1,380
Total allowance for loan losses	5,949	1,380	0	0
Recorded investment [Abstract]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	484,537	122,218
Total loans held for investment	484,537	122,218
Loans held for investment | Residential mortgage loans
Allowance for loan losses:
Individually evaluated for impairment	4,046	5,012
Collectively evaluated for impairment	8,480	9,338
Total allowance for loan losses	12,526	14,350	19,126	26,138
Recorded investment [Abstract]
Individually evaluated for impairment	62,706	65,793
Collectively evaluated for impairment	1,899,908	1,685,954
Total loans held for investment	1,962,614	1,751,747
Loans held for investment | SBL
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	2,966	2,049
Total allowance for loan losses	2,966	2,049	$ 1,115	$ 709
Recorded investment [Abstract]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,481,504	1,023,748
Total loans held for investment	$ 1,481,504	$ 1,023,748