Great Western Bancorp (GWB) 10-Q 14 May 15 2015 Q2 Quarterly report Financial data

Document

Document	6 Months Ended
	Mar. 31, 2015	Apr. 20, 2015
Document Information [Abstract]
Entity Registrant Name	Great Western Bancorp, Inc.
Entity Central Index Key	1613665
Current Fiscal Year End Date	-21
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding		57,886,114

Consolidated_Balance_Sheets_Un

Consolidated Balance Sheets (Unaudited) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Assets
Cash and due from banks	$358,440	$256,639
Securities available for sale	1,402,508	1,341,242
Investment in affiliates	1,683	1,683
Loans, net of allowance for loan losses of $52,426 and $47,518 at March 31, 2015 and September 30, 2014, respectively (includes $187,649 and $234,036 of loans covered by FDIC loss share agreements at March 31, 2015 and September 30, 2014, respectively, $1,060,598 and $985,411 of loans and written loan commitments carried at fair value under the fair value option at March 31, 2015 and September 30, 2014, respectively, and $9,006 and $10,381 of loans held for sale at March 31, 2015 and September 30, 2014, r	7,020,039	6,739,949
Premises and equipment	100,560	103,707
Accrued interest receivable	37,933	42,609
Other repossessed property (includes $8,575 and $10,628 of property covered under FDIC loss share agreements at March 31, 2015 and September 30, 2014, respectively)	43,565	49,580
FDIC indemnification asset	19,895	26,678
Goodwill	697,807	697,807
Core deposits and other intangibles	9,603	14,229
Net deferred tax assets	43,701	44,703
Other assets	45,911	52,603
Total assets	9,781,645	9,371,429
Deposits:
Noninterest-bearing	1,374,589	1,303,015
Interest-bearing	6,113,109	5,749,165
Total deposits	7,487,698	7,052,180
Securities sold under agreements to repurchase	163,343	161,687
FHLB advances and other borrowings	475,019	575,094
Related party notes payable	41,295	41,295
Subordinated debentures	56,083	56,083
Fair value of derivatives	48,814	13,092
Accrued interest payable	4,469	5,273
Income tax payable	0	4,915
Accrued expenses and other liabilities	35,372	40,720
Total liabilities	8,312,093	7,950,339
Stockholders' equity
Common stock, $0.01 par value, authorized 500,000,000 shares; issued and outstanding at March 31, 2015 and September 30, 2014 - 57,886,114 shares	579	579
Additional paid-in capital	1,260,844	1,260,124
Retained earnings	206,018	166,544
Accumulated other comprehensive income (loss)	2,111	-6,157
Total stockholders' equity	1,469,552	1,421,090
Total liabilities and stockholders' equity	$9,781,645	$9,371,429

Consolidated_Balance_Sheets_Un1

Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Allowance for loan losses	$52,426	$47,518
Loans covered by FDIC loss share agreements	187,649	234,036
Loans and written loan commitments at fair value under the fair value option	1,060,598	985,411
Loan held for sale	9,006	10,381
Property covered under FDIC loss share agreements	$8,575	$10,628
Common stock, par value (in USD per share)	$0.01	$0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	57,886,114	57,886,114
Common stock, shares outstanding	57,886,114	57,886,114

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Unaudited) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Interest and Fee Income, Loans and Leases [Abstract]
Loans	$82,394	$77,933	$166,738	$159,336
Taxable securities	5,379	6,623	11,066	13,592
Nontaxable securities	13	14	26	28
Dividends on securities	258	199	508	400
Federal funds sold and other	160	117	444	301
Total interest and dividend income	88,204	84,886	178,782	173,657
Interest expense
Deposits	5,984	6,431	11,999	13,310
Securities sold under agreements to repurchase	150	143	296	289
FHLB advances and other borrowings	893	803	1,839	1,840
Related party notes payable	227	226	459	460
Subordinated debentures and other	325	326	655	660
Total interest expense	7,579	7,929	15,248	16,559
Net interest income	80,625	76,957	163,534	157,098
Provision for loan losses	9,679	-2,690	12,998	-3,565
Net interest income after provision for loan losses	70,946	79,647	150,536	160,663
Noninterest income
Service charges and other fees	8,871	9,371	19,269	20,033
Net gain on sale of loans	1,580	947	3,124	2,563
Casualty insurance commissions	233	299	549	557
Investment center income	654	588	1,227	1,179
Net gain on sale of securities	0	6	51	6
Trust department income	938	1,000	2,006	1,905
Net increase (decrease) in fair value of loans at fair value	15,208	8,730	32,308	-380
Net realized and unrealized gain (loss) on derivatives	-21,698	-12,436	-46,303	-7,599
Other	1,150	1,635	2,605	2,702
Total noninterest income	6,936	10,140	14,836	20,966
Noninterest expense
Salaries and employee benefits	24,673	23,029	48,761	47,050
Occupancy expenses, net	3,984	4,486	8,008	8,719
Data processing	4,708	4,723	9,536	9,751
Equipment expenses	925	995	1,881	2,022
Advertising	946	1,088	1,674	2,172
Communication expenses	1,225	1,242	2,398	2,356
Professional fees	3,603	3,105	7,175	6,003
Net (gain) from sale of repossessed property and other assets	-16	-278	-384	-849
Amortization of core deposits and other intangibles	2,313	4,691	4,626	9,379
Other	6,077	6,246	11,854	11,023
Total noninterest expense	48,438	49,327	95,529	97,626
Income before income taxes	29,444	40,460	69,843	84,003
Provision for income taxes	9,720	14,489	23,422	29,428
Net income	19,724	25,971	46,421	54,575
Other comprehensive income (loss)bchange in net unrealized gain (loss) on securities available-for-sale (net of deferred income tax (expense) benefit of $(3,159) and $(3,693) for the three months ended March 31, 2015 and 2014, respectively and $(4,966) and $262 for the six months ended March 31, 2015 and 2014, respectively)	5,153	6,321	8,268	-133
Comprehensive income	24,877	32,292	54,689	54,442
Earnings per common share
Weighted average common shares outstanding	57,898,335	57,886,114	57,897,059	57,886,114
Basic earnings per share (in dollars per share)	$0.34	$0.45	$0.80	$0.94
Diluted earnings per common share
Weighted average shares outstanding (in shares)	57,916,802	57,886,114	57,906,293	57,886,114
Diluted earnings per share (in dollars per share)	$0.34	$0.45	$0.80	$0.94
Dividends per share
Dividends issued	$6,947	$34,000	$6,947	$34,000
Dividends per share (in dollars per share)	$0.12	$0.59	$0.12	$0.59

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Income tax (expense) benefit	($3,159)	($3,693)	($4,966)	$262

Consolidated_Statements_of_Sto

Consolidated Statements of Stockholders' Equity (Unaudited) (USD $)	Total	Comprehensive Income	Common Stock Par Value	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
In Thousands, unless otherwise specified
Beginning balance at Sep. 30, 2013	$1,417,214		$579	$1,260,124	$163,592	($7,081)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	54,575	54,575			54,575
Other comprehensive income (loss), net of tax:
Net change in net unrealized (loss) on securities available for sale	-133	-133				-133
Comprehensive income	54,442	54,442
Common stock, $0.59 and $.12 in FY 2014 and FY 2015, respectively	-34,000				-34,000
Ending balance at Mar. 31, 2014	1,437,656		579	1,260,124	184,167	-7,214
Beginning balance at Sep. 30, 2014	1,421,090		579	1,260,124	166,544	-6,157
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46,421	46,421			46,421
Other comprehensive income (loss), net of tax:
Net change in net unrealized (loss) on securities available for sale	8,268	8,268				8,268
Comprehensive income	54,689	54,689
Stock-based compensation	720			720
Common stock, $0.59 and $.12 in FY 2014 and FY 2015, respectively	-6,947				-6,947
Ending balance at Mar. 31, 2015	$1,469,552		$579	$1,260,844	$206,018	$2,111

Consolidated_Statements_of_Sto1

Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) (USD $)	6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Stockholders' Equity [Abstract]
Cash dividends paid on common stock (in USD per share)	$0.12	$0.59

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (Unaudited) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating activities
Net income	$46,421	$54,575
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	12,477	19,315
Net gain on sale of securities	-51	-6
Net gain on sale of loans	-3,124	-2,563
Net (gain) loss on sale of premises and equipment	-66	1,195
Net gain from sale of repossessed property and other assets	-384	-849
Provision for loan losses	12,998	-3,565
Provision for repossessed assets	4,324	2,125
Proceeds from FDIC indemnification claims	1,637	2,365
Stock-based compensation	720	0
Originations of residential real estate loans held-for-sale	-132,498	-84,951
Proceeds from sales of residential real estate loans held-for-sale	136,997	90,412
Net deferred income taxes	-4,066	-1,489
Changes in:
Accrued interest receivable	4,676	3,802
Other assets	2,579	1,896
FDIC indemnification asset	5,145	5,550
FDIC clawback liability	385	534
Accrued interest payable and other liabilities	24,272	-10,553
Net cash provided by operating activities	112,442	77,793
Investing activities
Purchase of securities available for sale	-238,828	0
Proceeds from sales and maturities of securities available for sale	187,457	158,816
Net increase in loans	-301,377	-207,963
Purchase of premises and equipment	-2,584	-1,624
Proceeds from sale of premises and equipment	1,438	515
Proceeds from sale of other assets	8,989	9,752
Redemption of FHLB stock	4,112	6,502
Net cash used in investing activities	-340,793	-34,002
Financing activities
Net increase in deposits	435,518	304,476
Net increase (decrease) in securities sold under agreements to repurchase	1,656	-12,769
Net decrease in FHLB advances and other borrowings	-100,075	-160,507
Dividends paid	-6,947	-34,000
Net cash provided by financing activities	330,152	97,200
Net increase in cash and due from banks	101,801	140,991
Cash and due from banks, beginning of period	256,639	282,157
Cash and due from banks, end of period	358,440	423,148
Supplemental disclosures of cash flows information
Cash payments for interest	16,052	17,790
Cash payments for income taxes	33,980	33,695
Supplemental schedules of noncash investing and financing activities
Loans transferred to repossessed assets and other assets	($6,914)	($30,829)

Basis_of_Presentation

Basis of Presentation	6 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation
	Great Western Bancorp, Inc. (the “Company”) is a bank holding company organized under the laws of Delaware. The primary business of the Company is ownership of its wholly owned subsidiary, Great Western Bank (the “Bank”). The Bank is a full-service regional bank focused on relationship-based business and agribusiness banking in Arizona, Colorado, Iowa, Kansas, Missouri, Nebraska, and South Dakota. The Company and the Bank are subject to the regulation of certain federal and/or state agencies and undergo periodic examinations by those regulatory authorities. Substantially all of the Company’s income is generated from banking operations. The Company was a majority owned indirect subsidiary of National Australia Bank Limited (“NAB”) at March 31, 2015.
	The accompanying unaudited consolidated interim financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) and reflect all adjustments that are, in the opinion of management, necessary for the fair presentation of the financial position and results of operations for the periods presented. All such adjustments are of a normal recurring nature other than the reclassifications outlined below.
	The unaudited interim consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements for the year ending September 30, 2014, which includes a description of significant accounting policies. The results of operations for interim periods are not necessarily indicative of the results that may be expected for the year or any other period.
	The accompanying unaudited consolidated financial statements include the accounts and results of operations of the Company and its subsidiaries after elimination of all significant intercompany accounts and transactions. The preparation of unaudited consolidated financial statements in conformity with U.S. GAAP requires management to make certain estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from these estimates.
	The Company has evaluated all events or transactions that occurred through the date the Company issued these financial statements. During this period, the Company did not have any material recognizable or non-recognizable subsequent events other than outlined below.
	On May 6, 2015, NAB sold 23.0 million shares of the Company's common stock, representing 39.7% of the Company's common stock, in the second stage of its planned divestment. After completion of the offering, NAB beneficially owns 28.5% of the Company's outstanding common stock.
	On April 28, 2015, the board of directors of the Company declared a dividend of $0.12 per common share payable on May 29, 2015 to owners of record as of close of business on May 15, 2015.
	Changes in the Presentation of Results for Loans at Fair Value and Related Derivatives
	In the normal course of business, the Company manages interest rate risk by entering into fixed-to-floating interest rate swaps related to all fixed-rate loans with original terms longer than five years. The Company has elected to account for these loans using the Fair Value Option. During the first quarter of fiscal year 2015, the Company identified an immaterial error in its reporting of one aspect of the derivatives related to these loans and also elected to change the presentation of the reported changes in fair value of these loans and related derivatives, each as discussed below. The Company's previous consolidated financial statements have been corrected or reclassified, as appropriate, to be consistent with the accompanying unaudited consolidated financial statements.
	During the first quarter of fiscal year 2015, the Company identified that the current realized gain (loss) on the derivatives related to fair value loans has been improperly recorded as loan interest income instead of being presented in the same line item as the unrealized gain (loss) on the derivatives. As such, the realized gain (loss) on the derivatives related to fair value loans has been moved from loan interest income to "Net realized and unrealized gain (loss) on derivatives" within noninterest income. The Company has determined these corrections to be immaterial to the prior period financial statements and there was no effect on net income, equity or cash flows. The following table reflects the impact of the matter described above on previously filed financial statements:
		Previously Reported			Currently Reported
		Interest Income			Noninterest Income
	Six months ended March 31, 2014
	Realized gain on derivatives	$	(8,678	)	$	(8,678	)
	Six months ended March 31, 2013
	Realized gain (loss) on derivatives	$	(6,668	)	$	(6,668	)
	Twelve months ended September 30, 2014
	Realized gain (loss) on derivatives	$	(18,255	)	$	(18,255	)
	Twelve months ended September 30, 2013
	Realized gain (loss) on derivatives	$	(14,217	)	$	(14,217	)
	Twelve months ended September 30, 2012
	Realized gain (loss) on derivatives	$	(9,931	)	$	(9,931	)
	Additionally, the Company previously reported the changes in fair value of these loans related to both interest rates and credit quality in interest income and the Company presented the changes in fair value of the derivatives in noninterest expense. Changes in fair value related to interest rates on the loans and changes in fair value of the derivatives were completely offset in any reporting period. To improve the clarity and comparability of its financial statements, the Company has elected to change its presentation of the changes in fair value related to these loans and derivatives by presenting these changes in two separate line items in noninterest income. As such, changes in fair value related to these loans, both related to interest rates and credit quality, is presented in "Net increase (decrease) in fair value of loans at fair value" within noninterest income, and changes in fair value related to these derivatives is presented in "Net realized and unrealized gain (loss) on derivatives" within noninterest income. The following table reflects the impact of the matter described above on previously filed financial statements:
		Previously Reported						Currently Reported
		Interest Income			Noninterest Expense			Noninterest Income
	Six months ended March 31, 2014
	Unrealized gain (loss) on derivatives	$	—		$	(1,078	)	$	—		$	(1,078	)
	Loan fair value change related to interest rates	1,078			—			1,078			—
	Loan fair value change related to credit quality	(698		)	—			(698		)	—
		$	380		$	(1,078	)	$	380		$	(1,078	)
	Six months ended March 31, 2013
	Unrealized gain (loss) on derivatives	$	—		$	(14,124	)	$	—		$	(14,124	)
	Loan fair value change related to interest rates	14,124			—			14,124			—
	Loan fair value change related to credit quality	(396		)	—			(396		)	—
		$	13,728		$	(14,124	)	$	13,728		$	(14,124	)
	Twelve months ended September 30, 2014
	Unrealized gain (loss) on derivatives	$	—		$	11,922		$	—		$	11,922
	Loan fair value change related to interest rates	(11,922		)	—			(11,922		)	—
	Loan fair value change related to credit quality	18			—			18			—
		$	(11,904	)	$	11,922		$	(11,904	)	$	11,922
	Twelve months ended September 30, 2013
	Unrealized gain (loss) on derivatives	$	—		$	(40,305	)	$	—		$	(40,305	)
	Loan fair value change related to interest rates	40,305			—			40,305			—
	Loan fair value change related to credit quality	855			—			855			—
		$	41,160		$	(40,305	)	$	41,160		$	(40,305	)
	Twelve months ended September 30, 2012
	Unrealized gain (loss) on derivatives	$	—		$	19,369		$	—		$	19,369
	Loan fair value change related to interest rates	(19,369		)	—			(19,369		)	—
	Loan fair value change related to credit quality	4,276			—			4,276			—
		$	(15,093	)	$	19,369		$	(15,093	)	$	19,369

New_Accounting_Pronouncements

New Accounting Pronouncements	6 Months Ended
	Mar. 31, 2015
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements	New Accounting Pronouncements
	There have been no new applicable accounting pronouncements issued during the six months ended March 31, 2015.

Restrictions_on_Cash_and_Due_f

Restrictions on Cash and Due from Banks	6 Months Ended
	Mar. 31, 2015
Cash and Cash Equivalents [Abstract]
Restrictions on Cash and Due from Banks	Restrictions on Cash and Due from Banks
	The Company is required to maintain reserve balances in cash and on deposit with the Federal Reserve based on a percentage of deposits. The total requirement was approximately $40.2 million and $50.4 million at March 31, 2015 and September 30, 2014, respectively.

Securities_Available_for_Sale

Securities Available for Sale	6 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Securities Available for Sale	Securities Available for Sale
	The amortized cost and approximate fair value of investments in securities, all of which are classified as available for sale according to management’s intent, are summarized as follows (in thousands):
		Amortized			Gross			Gross			Fair Value
					Unrealized			Unrealized
					Gains			Losses
	As of March 31, 2015
	U.S. Treasury securities	$	271,753		$	3,724		$	—		$	275,477
	U.S. Agency securities	74,345			456			—			74,801
	Mortgage-backed securities:
	Government National Mortgage Association	945,299			4,266			(4,469		)	945,096
	Federal National Mortgage Association	48,495			—			(129		)	48,366
	Small Business Assistance Program	51,086			—			(527		)	50,559
	States and political subdivision securities	2,107			1			—			2,108
	Corporate debt securities	4,996			66			—			5,062
	Other	1,006			33			—			1,039
		$	1,399,087		$	8,546		$	(5,125	)	$	1,402,508
		Amortized			Gross			Gross			Fair Value
					Unrealized			Unrealized
					Gains			Losses
	As of September 30, 2014
	U.S. Treasury securities	$	222,868		$	31		$	(174	)	$	222,725
	U.S. Agency securities	—			—			—			—
	Mortgage-backed securities:
	Government National Mortgage Association	1,113,363			4,639			(14,587		)	1,103,415
	Federal National Mortgage Association	—			—			—			—
	Small Business Assistance Program	—			—			—			—
	States and political subdivision securities	2,188			1			—			2,189
	Corporate debt securities	11,732			141			—			11,873
	Other	1,006			34			—			1,040
		$	1,351,157		$	4,846		$	(14,761	)	$	1,341,242
	The amortized cost and approximate fair value of debt securities available for sale as of March 31, 2015 and September 30, 2014, by contractual maturity, are shown below. Maturities of mortgage-backed securities may differ from contractual maturities because the mortgages underlying the securities may be called or repaid without any penalties.
		31-Mar-15						30-Sep-14
	(In Thousands)	Amortized Cost			Fair Value			Amortized Cost			Fair Value
	Due in one year or less	$	76,162		$	76,620		$	7,207		$	7,218
	Due after one year through five years	272,043			275,766			223,282			223,140
	Due after five years through ten years	4,996			5,062			6,299			6,429
		353,201			357,448			236,788			236,787
	Mortgage-backed securities	1,044,880			1,044,021			1,113,363			1,103,415
	Securities without contractual maturities	1,006			1,039			1,006			1,040
		$	1,399,087		$	1,402,508		$	1,351,157		$	1,341,242
	Proceeds from sales of securities available for sale were $0 and $4.5 million for the three months ended March 31, 2015 and 2014, respectively, and $55.1 million and $4.5 million for the six months ended March 31, 2015 and 2014, respectively. There were no gross gains or gross losses realized on sales for the three months ended March 31, 2015 and 2014, using the specific identification method. Gross gains of $0.6 million and $0 and gross losses of $0.5 million and $0 were realized on the sales for the six months ended March 31, 2015 and 2014, respectively, also using the specific identification method.
	Securities with a carrying value of approximately $1,174.9 million and $1,132.3 million at March 31, 2015 and September 30, 2014, respectively, were pledged as collateral on public deposits, securities sold under agreements to repurchase, and for other purposes as required or permitted by law. The counterparties do not have the right to sell or pledge the securities the Company has pledged as collateral.
	As detailed in the following tables, certain investments in debt securities, which are approximately 40% and 64% of the Company’s investment portfolio at March 31, 2015 and September 30, 2014, respectively, are reported in the consolidated financial statements at an amount less than their amortized cost. Based on evaluation of available evidence, including recent changes in market interest rates, credit rating information, implicit or explicit government guarantees, and information obtained from regulatory filings, management believes the declines in fair value of these securities are temporary. As the Company does not intend to sell the securities and it is not more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis, which may be maturity, the Company does not consider the securities to be other than temporarily impaired at March 31, 2015 or September 30, 2014. The Company did not recognize any other-than-temporary impairment for the three and six months ended March 31, 2015 and 2014.
	The following table presents the Company’s gross unrealized losses and approximate fair value in investments, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position (in thousands):
		Less than 12 months						March 31, 2015						Total
								12 months or more
		Fair Value			Unrealized			Fair Value			Unrealized			Fair Value		Unrealized
	U.S. Treasury securities	$	—		$	—		$	—		$	—		$	—	$	—
	U. S. Agency securities	—			—			—			—			$	—	$	—
	Mortgage-backed securities	83,704			(656		)	479,290			(4,469		)	562,994		(5,125		)
	Corporate debt securities	—			—			—			—			—		—
	Other	—			—			—			—			—		—
		$	83,704		$	(656	)	$	479,290		$	(4,469	)	$	562,994	$	(5,125	)
		Less than 12 months						September 30, 2014						Total
								12 months or more
		Fair Value			Unrealized			Fair Value			Unrealized			Fair Value		Unrealized
	U.S. Treasury securities	$	98,344		$	(174	)	$	—		$	—		$	98,344	$	(174	)
	U.S. Agency securities	—			—			—			—			$	—	$	—
	Mortgage-backed securities	24,625			(125		)	730,171			(14,462		)	754,796		(14,587		)
	Corporate debt securities	—			—			—			—			—		—
	Other	—			—			—			—			—		—
		$	122,969		$	(299	)	$	730,171		$	(14,462	)	$	853,140	$	(14,761	)
	The Company’s investments in nonmarketable equity securities are all stock of the Federal Home Loan Bank ("FHLB"). The carrying value of Federal Home Loan Bank stock was $31.8 million and $35.9 million as of March 31, 2015 and September 30, 2014, respectively, and is reported in other assets on the consolidated balance sheets. No indicators of impairment related to FHLB stock were identified during the three and six months ended March 31, 2015 and 2014.
	The components of other comprehensive income from net unrealized gains (losses) on securities available for sale for the three and six months ended March 31, 2015 and 2014, respectively are as follows (in thousands):
	Three Months Ended						Six Months Ended March 31,
	March 31,
	2015			2014			2015			2014
Beginning balance accumulated other comprehensive income (loss)	$	(3,042	)	$	(13,535	)	$	(6,157	)	$	(7,081	)
Net unrealized holding gain (loss) arising during the period	8,312			10,020			13,285			(389		)
Reclassification adjustment for net gain realized in net income	—			(6		)	(51		)	(6		)
Net change in unrealized gain (loss) before income taxes	8,312			10,014			13,234			(395		)
Income tax (expense) benefit	(3,159		)	(3,693		)	(4,966		)	262
Net change in unrealized gain (loss) on securities after taxes	5,153			6,321			8,268			(133		)
Ending balance accumulated other comprehensive income (loss)	$	2,111		$	(7,214	)	$	2,111		$	(7,214	)

Loans

Loans	6 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Loans	Loans
	The composition of net loans as of March 31, 2015 and September 30, 2014, is as follows (in thousands):
		March 31, 2015				September 30, 2014
	Residential real estate	$	905,114			$	901,605
	Commercial real estate	2,673,255				2,541,194
	Commercial non real estate	1,657,856				1,571,640
	Agriculture	1,748,366				1,681,209
	Consumer	80,036				90,086
	Other	35,433				34,243
		7,100,060				6,819,977
	Less:
	Allowance for loan losses	(52,426		)		(47,518		)
	Unamortized discount on acquired loans	(21,774		)		(25,638		)
	Unearned net deferred fees and costs and loans in process	(5,821		)		(6,872		)
		$	7,020,039			$	6,739,949
	The loan breakouts above include loans covered by FDIC loss sharing agreements totaling $187.6 million and $234.0 million as of March 31, 2015 and September 30, 2014, respectively, residential real estate loans held for sale totaling $9.0 million and $10.4 million at March 31, 2015 and September 30, 2014, respectively, and $1,060.6 million and $985.4 million of loans and written loan commitments accounted for at fair value as of March 31, 2015 and September 30, 2014, respectively.
	Unamortized net deferred fees and costs totaled $6.5 million and $6.3 million as of March 31, 2015 and September 30, 2014, respectively.
	Loans in process represent loans that have been funded as of the balance sheet dates but not classified into a loan category and loan payments received as of the balance sheet dates that have not been applied to individual loan accounts. Loans in process totaled $(0.7) million and $0.6 million as of March 31, 2015 and September 30, 2014, respectively.
	Loans guaranteed by agencies of the U.S. government totaled $112.3 million and $106.5 million at March 31, 2015 and September 30, 2014, respectively.
	Principal balances of residential real estate loans sold totaled $69.6 million and $33.7 million for the three months ended March 31, 2015 and 2014, respectively and $133.9 million and $87.8 million for the six months ended March 31, 2015 and 2014, respectively.
	The following table presents the Company’s nonaccrual loans at March 31, 2015 and September 30, 2014 (in thousands), excluding loans covered under the FDIC loss-sharing agreements. Loans greater than 90 days past due and still accruing interest as of March 31, 2015 and September 30, 2014, were not significant.
	Nonaccrual loans	March 31, 2015				September 30, 2014
	Residential real estate	$	7,690			$	6,671
	Commercial real estate	10,836				20,767
	Commercial non real estate	9,015				4,908
	Agriculture	18,860				11,453
	Consumer	111				146
	Total	$	46,512			$	43,945
	The following table (in thousands) presents the Company’s past due loans at March 31, 2015 and September 30, 2014. This table is presented net of unamortized discount on acquired loans and excludes loans measured at fair value with changes in fair value reported in earnings of $1,060.6 million for March 31, 2015 and $985.4 million for September 30, 2014.
	As of March 31, 2015	30-59 Days				60-89 Days				Greater Than				Total				Current				Total
		Past Due				Past Due				90 Days				Past Due								Financing
																						Receivables
	Residential real estate	$	1,909			$	562			$	2,854			$	5,325			$	777,219			$	782,544
	Commercial real estate	165				2,316				4,816				7,297				2,284,882				2,292,179
	Commercial non real estate	3,344				622				4,262				8,228				1,221,359				1,229,587
	Agriculture	3,491				—				834				4,325				1,406,083				1,410,408
	Consumer	218				28				35				281				79,603				79,884
	Other	—				—				—				—				35,433				35,433
		9,127				3,528				12,801				25,456				5,804,579				5,830,035
	Loans covered by FDIC loss sharing agreements	4,744				214				2,768				7,726				179,923				187,649
	Total	$	13,871			$	3,742			$	15,569			$	33,182			$	5,984,502			$	6,017,684
	As of September 30, 2014	30-59 Days				60-89 Days				90 Days or Greater Past Due				Total				Current				Total
		Past Due				Past Due								Past Due								Financing
																						Receivables
	Residential real estate	$	675			$	611			$	2,581			$	3,867			$	760,887			$	764,754
	Commercial real estate	11,050				819				3,384				15,253				1,988,585				2,003,838
	Commercial non real estate	1,761				6,228				744				8,733				1,303,925				1,312,658
	Agriculture	16				368				4,205				4,589				1,364,960				1,369,549
	Consumer	244				18				49				311				89,528				89,839
	Other	—				—				—				—				34,243				34,243
		13,746				8,044				10,963				32,753				5,542,128				5,574,881
	Loans covered by FDIC loss sharing agreements	1,960				1,252				3,728				6,940				227,096				234,036
	Total	$	15,706			$	9,296			$	14,691			$	39,693			$	5,769,224			$	5,808,917
	The composition of the loan portfolio by internally assigned grade is as follows as of March 31, 2015 and September 30, 2014. This table (in thousands) is presented net of unamortized discount on acquired loans and excludes loans measured at fair value with changes in fair value reported in earnings of $1,060.6 million for March 31, 2015 and $985.4 million for September 30, 2014:
	As of March 31, 2015	Residential				Commercial				Commercial				Agriculture				Consumer				Other		Total
		Real Estate				Real Estate				Non Real
										Estate
	Credit Risk Profile by Internally Assigned Grade
	Grade:
	Pass	$	765,058			$	2,122,618			$	1,093,867			$	1,188,111			$	79,244			$	35,433	$	5,284,331
	Watchlist	5,248				105,838				96,724				176,266				372				—		384,448
	Substandard	11,759				63,540				36,627				44,290				259				—		156,475
	Doubtful	428				183				2,369				1,741				1				—		4,722
	Loss	51				—				—				—				8				—		59
Ending balance	782,544				2,292,179				1,229,587				1,410,408				79,884				35,433		5,830,035
Loans covered by FDIC loss sharing agreements	113,578				63,268				8,925				1,832				46				—		187,649
Total	$	896,122			$	2,355,447			$	1,238,512			$	1,412,240			$	79,930			$	35,433	$	6,017,684
As of September 30, 2014	Residential				Commercial				Commercial				Agriculture				Consumer				Other		Total
	Real Estate				Real Estate				Non Real
									Estate
Credit Risk Profile by Internally Assigned Grade
Grade:
Pass	$	747,485			$	1,867,866			$	1,218,558			$	1,202,145			$	89,197			$	34,243	$	5,159,494
Watchlist	5,320				84,132				65,628				132,262				381				—		287,723
Substandard	11,290				51,692				27,499				35,107				242				—		125,830
Doubtful	659				148				798				35				19				—		1,659
Loss	—				—				175				—				—				—		175
Ending balance	764,754				2,003,838				1,312,658				1,369,549				89,839				34,243		5,574,881
Loans covered by FDIC loss sharing agreements	127,115				95,467				9,390				2,004				60				—		234,036
Total	$	891,869			$	2,099,305			$	1,322,048			$	1,371,553			$	89,899			$	34,243	$	5,808,917
Impaired Loans
The following table presents the Company’s impaired loans (in thousands). This table excludes loans covered by FDIC loss sharing agreements:
	Recorded				Unpaid				Related				Average
	Investment				Principal				Allowance				Recorded
					Balance								Investment
As of March 31, 2015
Impaired loans:
With an allowance recorded:
Residential real estate	$	12,332			$	12,452			$	2,721			$	12,220
Commercial real estate	73,729				75,381				1,753				67,942
Commercial non real estate	41,310				49,834				6,905				36,916
Agriculture	46,031				46,059				3,007				40,780
Consumer	268				325				52				274
	$	173,670			$	184,051			$	14,438			$	158,132
	Recorded				Unpaid				Related				Average
	Investment				Principal				Allowance				Recorded
					Balance								Investment
As of September 30, 2014
Impaired loans:
With an allowance recorded:
Residential real estate	$	12,107			$	12,737			$	2,529			$	13,572
Commercial real estate	62,155				64,597				2,017				84,490
Commercial non real estate	32,522				37,882				3,927				31,827
Agriculture	35,528				37,958				1,155				30,546
Consumer	280				491				51				346
	$	142,592			$	153,665			$	9,679			$	160,781
There are no impaired loans without a valuation allowance, other than those loans for which the Company has claim to collateral with value(s) in excess of the outstanding loan amount, after allowing for the cost of liquidating the collateral as of March 31, 2015 and September 30, 2014. Interest income recognized on impaired loans for the three months ended March 31, 2015 and 2014 totaled $1.8 million and $2.1 million, respectively and $4.8 million and $3.3 million for the six months ended March 31, 2015 and 2014, respectively.
Valuation adjustments made to repossessed properties for the three months ended March 31, 2015 and 2014, totaled $2.2 million and $0.5 million, respectively, and $4.3 million and $1.0 million for the six months ended March 31, 2015 and 2014, respectively. The adjustments are included in other noninterest expense.
Troubled Debt Restructured Loans
Included in certain loan categories in the impaired loans are troubled debt restructurings (“TDRs”) that were classified as impaired. These TDRs do not include purchased impaired loans. When the Company grants concessions to borrowers such as reduced interest rates or extensions of loan periods that would not be considered other than because of borrowers’ financial difficulties, the modification is considered a TDR. Specific reserves included in the allowance for loan losses for TDRs were $2.7 million and $3.2 million at March 31, 2015 and September 30, 2014, respectively. Commitments to lend additional funds to borrowers whose loans were modified in a TDR were not significant as of March 31, 2015 or September 30, 2014.
The following table presents the recorded value of the Company’s TDR balances as of March 31, 2015 and September 30, 2014 (in thousands):
	31-Mar-15								30-Sep-14
	Accruing				Nonaccrual				Accruing				Nonaccrual
Residential real estate	$	618			$	1,929			$	1,112			$	1,730
Commercial real estate	45,160				5,424				25,177				6,884
Commercial non real estate	10,165				1,445				6,753				1,785
Agriculture	2,159				6,377				3,780				9,994
Consumer	20				13				35				22
Total	$	58,122			$	15,188			$	36,857			$	20,415
The following table presents a summary of all accruing loans restructured in TDRs during the three months ended March 31, 2015 and 2014, respectively:
	Three Months Ended March 31,
	2015											2014
				Recorded Investment											Recorded Investment
($ in thousands)	Number			Pre-				Post-				Number			Pre-				Post-
				Modification				Modification							Modification				Modification
Residential real estate
Rate modification	1			$	15			$	15			—			$	—			$	—
Term extension	—			—				—				—			—				—
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	1			21				21				—			—				—
Total residential real estate	2			36				36				—			—				—
Commercial real estate
Rate modification	—			—				—				—			—				—
Term extension	1			90				—				—			—				—
Payment modification	4			3,660				3,660				—			—				—
Bankruptcy	1			498				498				—			—				—
Other	—			—				—				—			—				—
Total commercial real estate	6			4,248				4,158				—			—				—
Commercial non real estate
Rate modification	—			—				—				—			—				—
Term extension	3			2,879				2,879				1			35				35
Payment modification	1			50				50				2			67				67
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				1			327				327
Total commercial non real estate	4			2,929				2,929				4			429				429
Agriculture
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				—			—				—
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				—			—				—
Total agriculture	—			—				—				—			—				—
Consumer
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				—			—				—
Payment modification	—			—				—				2			4				4
Bankruptcy	1			6				6				—			—				—
Other	—			—				—				1			18				18
Total consumer	1			6				6				3			22				22
Total accruing	13			$	7,219			$	7,129			7			$	451			$	451
Change in recorded investment due to principal paydown at time of modification	—			—								—			—				—
Change in recorded investment due to chargeoffs at time of modification	1			90				—				—			—				—
The following table presents a summary of all accruing loans restructured in TDRs during the six months ended March 31, 2015 and 2014:
	Six Months Ended March 31,
	2015											2014
				Recorded Investment											Recorded Investment
($ in thousands)	Number			Pre-				Post-				Number			Pre-				Post-
				Modification				Modification							Modification				Modification
Residential real estate
Rate modification	1			$	15			$	15			—			$	—			$	—
Term extension	—			—				—				2			74				74
Payment modification	—			—				—				1			15				15
Bankruptcy	—			—				—				1			130				130
Other	1			21				21				—			—				—
Total residential real estate	2			36				36				4			219				219
Commercial real estate
Rate modification	—			—				—				—			—				—
Term extension	1			90				—				—			—				—
Payment modification	6			22,542				22,542				1			1,070				1,070
Bankruptcy	1			498				498				—			—				—
Other	—			—				—				—			—				—
Total commercial real estate	8			23,130				23,040				1			1,070				1,070
Commercial non real estate
Rate modification	1			32				32				—			—				—
Term extension	3			2,879				2,879				4			1,734				1,734
Payment modification	2			1,874				1,874				4			735				735
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				1			327				327
Total commercial non real estate	6			4,785				4,785				9			2,796				2,796
Agriculture
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				—			—				—
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				—			—				—
Total agriculture	—			—				—				—			—				—
Consumer
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				—			—				—
Payment modification	—			—				—				2			4				4
Bankruptcy	1			6				6				—			—				—
Other	—			—				—				2			28				28
Total consumer	1			6				6				4			32				32
Total accruing	17			27,957				27,867				18			$	4,117			$	4,117
Change in recorded investment due to principal paydown at time of modification	—			—								—			—				—
Change in recorded investment due to chargeoffs at time of modification	1			90				—				—			—				—
The following table presents a summary of all non-accruing loans restructured in TDRs during the three months ended March 31, 2015 and 2014:
	Three Months Ended March 31,
	2015											2014
				Recorded Investment											Recorded Investment
($ in thousands)	Number			Pre-				Post-				Number			Pre-				Post-
				Modification				Modification							Modification				Modification
Residential real estate
Rate modification	2			$	104			$	104			4			$	98			$	98
Term extension	1			77				77				1			15				15
Payment modification	—			—				—				—			—				—
Bankruptcy	1			43				43				—			—				—
Other	—			—				—				—			—				—
Total residential real estate	4			224				224				5			113				113
Commercial real estate
Rate modification	—			—				—				2			500				500
Term extension	—			—				—				2			4,031				4,031
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				1			87				87
Total commercial real estate	—			—				—				5			4,618				4,618
Commercial Non Real Estate
Rate modification	—			—				—				—			—				—
Term extension	4			217				217				—			—				—
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				1			10				10
Other	—			—				—				—			—				—
Total commercial non real estate	4			217				217				1			10				10
Agriculture
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				2			260				260
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				—			—				—
Total agriculture	—			—				—				2			260				260
Consumer
Rate modification	—			—				—				—			—				—
Term extension	1			1				1				—			—				—
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				—			—				—
Total consumer	1			1				1				—			—				—
Total non-accruing	9			$	442			$	442			13			$	5,001			$	5,001
Change in recorded investment due to principal paydown at time of modification	—			—				—				—			—				—
Change in recorded investment due to chargeoffs at time of modification	—			—				—				—			—				—
The following table presents a summary of all non-accruing loans restructured in TDRs during the six months ended March 31, 2015 and 2014:
	Six Months Ended March 31,
	2015											2014
				Recorded Investment											Recorded Investment
($ in thousands)	Number			Pre-				Post-				Number			Pre-				Post-
				Modification				Modification							Modification				Modification
Residential real estate
Rate modification	2			$	104			$	104			4			$	98			$	98
Term extension	1			77				77				2			18				18
Payment modification	—			—				—				—			—				—
Bankruptcy	1			43				43				1			4				4
Other	—			—				—				1			38				38
Total residential real estate	4			224				224				8			158				158
Commercial real estate
Rate modification	—			—				—				2			500				500
Term extension	—			—				—				2			4,031				4,031
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				1			87				87
Total commercial real estate	—			—				—				5			4,618				4,618
Commercial Non Real Estate
Rate modification	—			—				—				—			—				—
Term extension	4			217				217				8			125				125
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				1			10				10
Other	—			—				—				—			—				—
Total commercial non real estate	4			217				217				9			135				135
Agriculture
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				2			260				260
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				—			—				—
Total agriculture	—			—				—				2			260				260
Consumer
Rate modification	—			—				—				—			—				—
Term extension	1			1				1				1			11				11
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				1			1				1
Total consumer	1			1				1				2			12				12
Total non-accruing	9			442				442				26			$	5,183			$	5,183
Change in recorded investment due to principal paydown at time of modification	—			—				—				—			—				—
Change in recorded investment due to chargeoffs at time of modification	—			—				—				—			—				—
The tables below represent defaults on loans that were first modified during the respective past 12 months, that became 90 days or more delinquent or were charged-off during the three and six months ended March 31, 2015 and 2014, respectively.
	Three Months Ended
	March 31,
	2015							2014
($ in thousands)	Number of			Recorded				Number of			Recorded
	Loans			Investment				Loans			Investment
Residential real estate	4			$	107			3			$	375
Commercial real estate	—			—				3			1,814
Commercial non real estate	—			—				5			1,604
Agriculture	—			—				6			3,685
Consumer	—			—				—			—
	4			$	107			17			$	7,478
	Six Months Ended
	March 31,
	2015							2014
($ in thousands)	Number of			Recorded				Number of			Recorded
	Loans			Investment				Loans			Investment
Residential real estate	10			$	629			3			$	375
Commercial real estate	—			—				5			8,110
Commercial non real estate	1			95				5			1,604
Agriculture	1			15				7			7,361
Consumer	—			—				—			—
	12			$	739			20			$	17,450
The majority of loans that were modified and subsequently became 90 days or more delinquent have remained on nonaccrual status since the time of modification.

Allowance_for_Loan_Losses

Allowance for Loan Losses	6 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Allowance for Loan Losses	Allowance for Loan Losses
	The following tables presents the Company’s allowance for loan losses roll forward for the three and six month periods ended March 31, 2015 and 2014.
	Three Months Ended March 31, 2015	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Beginning balance January 1,	$	7,567		$	17,722		$	14,625		$	10,920		$	201		$	785		$	51,820
	2015
	Charge-offs	(63		)	(1,570		)	(8,440		)	(27		)	(19		)	(403		)	(10,522		)
	Recoveries	70			26			983			22			23			325			1,449
	Provision	160			(389		)	8,789			1,307			(17		)	120			9,970
	(Impairment) improvement of	(239		)	(53		)	—			—			1			—			(291		)
	loans acquired with
	deteriorated credit quality
	Ending balance March 31, 2015	$	7,495		$	15,736		$	15,957		$	12,222		$	189		$	827		$	52,426
	Three Months Ended March 31, 2014	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Beginning balance January 1, 2014	$	11,854		$	22,292		$	11,552		$	9,256		$	390		$	725		$	56,069
	Charge-offs	(207		)	(3,194		)	(838		)	(2,086		)	(96		)	(486		)	(6,907		)
	Recoveries	21			433			(128		)	(2		)	31			326			681
	Provision	(216		)	(2,536		)	1,380			735			37			100			(500		)
	(Impairment) improvement of	(1,175		)	608			(1,691		)	—			68			—			(2,190		)
	loans acquired with
	deteriorated credit quality
	Ending balance March 31, 2014	$	10,277		$	17,603		$	10,275		$	7,903		$	430		$	665		$	47,153
	Six Months Ended March 31, 2015	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Beginning balance October 1,	$	8,342		$	16,884		$	10,550		$	10,655		$	264		$	823		$	47,518
	2014
	Charge-offs	(120		)	(1,652		)	(8,524		)	(27		)	(57		)	(831		)	(11,211		)
	Recoveries	113			95			2,143			79			47			644			3,121
	Provision	(190		)	346			11,788			1,515			(41		)	191			13,609
	(Impairment) improvement of	(650		)	63			—			—			(24		)	—			(611		)
	loans acquired with
	deteriorated credit quality
	Ending balance March 31, 2015	$	7,495		$	15,736		$	15,957		$	12,222		$	189		$	827		$	52,426
	Six Months Ended March 31, 2014	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Beginning balance October 1,	$	11,779		$	22,562		$	11,222		$	9,296		$	312		$	693		$	55,864
	2013
	Charge-offs	(437		)	(3,194		)	(999		)	(2,086		)	(152		)	(956		)	(7,824		)
	Recoveries	96			1,024			759			15			67			717			2,678
	Provision	14			(3,397		)	734			678			135			211			(1,625		)
	(Impairment) improvement of	(1,175		)	608			(1,441		)	—			68			—			(1,940		)
	loans acquired with
	deteriorated credit quality
	Ending balance March 31, 2014	$	10,277		$	17,603		$	10,275		$	7,903		$	430		$	665		$	47,153
	The following tables provide details regarding the allowance for loan and lease losses and balance by type of allowance. These tables (in thousands) are presented net of unamortized discount on acquired loans and excludes loans measured at fair value with changes in fair value reported in earnings of $1,060.6 million, loans held for sale of $9.0 million, and guaranteed loans of $112.3 million for March 31, 2015 and loans measured at fair value with changes in fair value reported in earnings of $985.4 million, loans held for sale of $10.4 million, and guaranteed loans of $106.5 million for September 30, 2014.
	As of March 31, 2015	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Allowance for loan losses
	Individually evaluated for impairment	$	2,721		$	1,691		$	6,894		$	3,007		$	52		$	—		$	14,365
	Collectively evaluated for impairment	2,640			11,274			9,063			9,215			137			827			33,156
	Loans acquired with deteriorated credit quality	2,134			709			—			—			—			—			2,843
	Loans acquired without deteriorated credit quality	—			2,062			—			—			—			—			2,062
	Total allowance	$	7,495		$	15,736		$	15,957		$	12,222		$	189		$	827		$	52,426
	Financing Receivables
	Individually evaluated for impairment	$	9,669		$	62,020		$	39,900		$	36,407		$	177		$	—		$	148,173
	Collectively evaluated for impairment	677,091			2,138,649			1,134,073			1,350,998			76,625			35,433			5,412,869
	Loans acquired with deteriorated credit quality	93,277			27,834			5,348			1,595			1,466			—			129,520
	Loans acquired without deteriorated credit quality	105,259			74,794			8,026			16,102			1,662			—			205,843
Loans Outstanding	$	885,296		$	2,303,297		$	1,187,347		$	1,405,102		$	79,930		$	35,433		$	5,896,405
As of September 30, 2014	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
	Real Estate			Real Estate			Non Real
							Estate
Allowance for loan losses
Individually evaluated for impairment	$	2,528		$	1,953		$	3,909		$	1,152		$	51		$	—		$	9,593
Collectively evaluated for impairment	3,030			12,034			6,641			9,503			188			823			32,219
Loans acquired with deteriorated credit quality	2,784			645			—			—			25			—			3,454
Loans acquired without deteriorated credit quality	—			2,252			—			—			—			—			2,252
Total allowance	$	8,342		$	16,884		$	10,550		$	10,655		$	264		$	823		$	47,518
Financing Receivables
Individually evaluated for impairment	$	9,384		$	38,457		$	28,298		$	25,655		$	166		$	—		$	101,960
Collectively evaluated for impairment	649,970			1,874,474			1,224,035			1,319,343			85,065			34,243			5,187,130
Loans acquired with deteriorated credit quality	102,987			49,202			6,361			1,746			1,843			—			162,139
Loans acquired without deteriorated credit quality	117,630			95,323			7,409			17,655			2,825			—			240,842
Loans Outstanding	$	879,971		$	2,057,456		$	1,266,103		$	1,364,399		$	89,899		$	34,243		$	5,692,071
The reserve for unfunded loan commitments was $0.4 million at both March 31, 2015 and September 30, 2014.

Accounting_for_Certain_Loans_A

Accounting for Certain Loans Acquired with Deteriorated Credit Quality	6 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Accounting for Certain Loans Acquired with Deteriorated Credit Quality	Accounting for Certain Loans Acquired with Deteriorated Credit Quality
	In June 2010, the Company acquired certain loans that had deteriorated credit quality. Loan accounting specific to these purchased impaired loans addresses differences between contractual cash flows expected to be collected from the initial investment in loans if those differences are attributable, at least in part, to credit quality. Several factors were considered when evaluating whether a loan was considered a purchased impaired loan, including the delinquency status of the loan, updated borrower credit status, geographic information, and updated loan-to-values (“LTV”). U.S. GAAP allows purchasers to aggregate purchased impaired loans acquired in the same fiscal quarter in one or more pools, provided that the loans have common risk characteristics. A pool is then accounted for as a single asset with a single composite interest rate and an aggregate expectation of cash flows.
	Loan pools are periodically reassessed to determine expected cash flows. In determining the expected cash flows, the timing of cash flows and prepayment assumptions for smaller, homogenous loans are based on statistical models that take into account factors such as the loan interest rate, credit profile of the borrowers, the years in which the loans were originated, and whether the loans are fixed or variable rate loans. Prepayments may be assumed on large individual loans that consider similar prepayment factors listed above for smaller homogenous loans. The re-assessment of purchased impaired loans resulted in the following changes in the accretable yield during the three and six months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Balance at beginning of period	$	46,342		$	58,411		$	50,889		$	67,660
	Accretion	(3,222		)	(4,944		)	(8,009		)	(9,374		)
	Reclassification from nonaccretable difference	311			2,948			631			2,948
	Disposals	—			—			(80		)	(4,819		)
	Balance at end of period	43,431			56,415			43,431			56,415
	The reclassifications from nonaccretable difference noted in the table above represent instances where specific pools of loans are expected to perform better over the remaining lives of the loans than expected at the prior re-assessment date.
	The following table provides purchased impaired loans at March 31, 2015 and September 30, 2014 (in thousands):
		March 31, 2015									30-Sep-14
		Outstanding			Recorded			Carrying			Outstanding			Recorded		Carrying
		Balance 1			Investment 2			Value 3			Balance 1			Investment 2		Value 3
	Residential real estate	$	110,499		$	93,277		$	91,143		$	115,863		$	102,987	$	100,203
	Commercial real estate	107,514			27,835			27,126			130,825			49,202		48,557
	Commercial non real estate	14,710			5,348			5,348			16,697			6,361		6,361
	Agriculture	1,623			1,595			1,595			1,747			1,746		1,746
	Consumer	1,838			1,466			1,466			2,019			1,843		1,818
	Total lending	$	236,184		$	129,521		$	126,678		$	267,151		$	162,139	$	158,685
	1    Represents the legal balance of loans acquired with deteriorated credit quality.
	2    Represents the book balance of loans acquired with deteriorated credit quality.
	3    Represents the book balance of loans acquired with deteriorated credit quality net of the related allowance for loan losses.
	Due to improved cash flows of the purchased impaired loans, the reductions to allowance recognized on previous impairments were $0.4 million and $3.6 million for the three months ended March 31, 2015 and 2014, respectively and $0.9 million and $3.6 million for the six months ended March 31, 2015 and 2014, respectively.

FDIC_Indemnification_Asset

FDIC Indemnification Asset	6 Months Ended
	Mar. 31, 2015
Banking and Thrift [Abstract]
FDIC Indemnification Asset	FDIC Indemnification Asset
	Under the terms of the purchase and assumption agreement with the FDIC with regard to the TierOne Bank acquisition, the Company is reimbursed for a portion of the losses incurred on covered assets. As covered assets are resolved, whether it be through repayment, short sale of the underlying collateral, the foreclosure on or sale of collateral, or the sale or charge-off of loans or OREO, any differences between the carrying value of the covered assets versus the payments received during the resolution process, that are reimbursable by the FDIC, are recognized as reductions in the FDIC indemnification asset. Any gains or losses realized from the resolution of covered assets reduce or increase, respectively, the amount recoverable from the FDIC. The following table represents a summary of the activity related to the FDIC indemnification asset for the three and six months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Balance at beginning of period	$	22,162		$	41,756		$	26,678		$	45,690
	Amortization	(2,060		)	(4,662		)	(4,593		)	(7,947		)
	Changes in expected reimbursements from FDIC for changes in expected credit losses	2			(382		)	(190		)	(408		)
	Changes in reimbursable expenses	(207		)	1,437			(363		)	2,805
	Payments to/(from) the FDIC	(2		)	(374		)	(1,637		)	(2,365		)
	Balance at end of period	$	19,895		$	37,775		$	19,895		$	37,775
	The loss claims filed are subject to review, approval, and annual audits by the FDIC or its assigned agents for compliance with the terms in the loss sharing agreements.

Derivative_Financial_Instrumen

Derivative Financial Instruments	6 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments
	In the normal course of business, the Company uses interest rate swaps to manage its interest rate risk and market risk in accommodating the needs of its customers. Also, the Company enters into interest rate lock commitments on mortgage loans to be held for sale, with corresponding forward sales contracts related to these interest rate lock commitments.
	Derivative instruments are recognized as either assets or liabilities in the accompanying consolidated financial statements and are measured at fair value.
	The following table summarizes the notional amounts and estimated fair values of the Company’s derivative instruments at March 31, 2015 and September 30, 2014 (in thousands).
		March 31, 2015
		Notional				Balance Sheet		Positive Fair				Negative Fair
		Amount				Location		Value				Value
	Derivatives not designated as hedging instruments:
	Interest rate swaps	$	1,045,934			Liabilities		$	71			$	(48,858	)
	Mortgage loan commitments	37,394				Assets		27				—
	Mortgage loan forward sale contracts	44,485				Liabilities		—				(27		)
		September 30, 2014
		Notional				Balance Sheet		Positive Fair				Negative Fair
		Amount				Location		Value				Value
	Derivatives not designated as hedging instruments:
	Interest rate swaps	$	986,440			Liabilities		$	6,213			$	(19,286	)
	Mortgage loan commitments	22,563				Assets		19				—
	Mortgage loan forward sale contracts	28,459				Liabilities		—				(19		)
	As with any financial instrument, derivative financial instruments have inherent risk including adverse changes in interest rates. The Company’s exposure to derivative credit risk is defined as the possibility of sustaining a loss due to the failure of the counterparty to perform in accordance with the terms of the contract. Credit risks associated with interest rate swaps is similar to those relating to traditional on-balance sheet financial instruments. The Company manages interest rate swap credit risk with the same standards and procedures applied to its commercial lending activities. Amounts due from NAB to reclaim cash collateral under the interest rate swap master netting arrangements have not been offset against the derivative balances. These receivables are classified on the consolidated balance sheets as cash and were $0 as of March 31, 2015 and September 30, 2014, respectively.
	The effect of derivatives on the consolidated statements of comprehensive income for the three and six months ended March 31, 2015 and 2014 (in thousands) was as follows:
				Amount of Gain (Loss) Recognized in Income
				Three Months Ended								Six Months Ended
		Location of		March 31, 2015				March 31, 2014				March 31, 2015				March 31, 2014
		Gain (Loss) Recognized in
		Income
	Derivatives not designated as hedging instruments:
	Interest rate swaps	Noninterest income		$	(21,698	)		$	(12,436	)		$	(46,303	)		$	(7,599	)
	Mortgage loan commitments	Noninterest income		13				31				27				34
	Mortgage loan forward sale contracts	Noninterest income		(13		)		(31		)		(27		)		(34		)
	Netting of Derivatives
	The Company has various financial assets and financial liabilities that are subject to enforceable master netting agreements or similar agreements. The Company has entered into an ISDA master netting arrangement with NAB. Under the terms of the master netting arrangements, all transactions between the Company and the counterparty constitute a single business relationship such that in the event of default, the non-defaulting party is entitled to set off claims and apply property held by that party in respect of any transaction against obligations owed. Any payments, deliveries, or other transfers may be applied against each other and netted.
	The table below shows total gross derivative assets and liabilities which are adjusted on an aggregate basis, where applicable to take into consideration the effects of legally enforceable master netting agreements for the net reported amount in the consolidated balance sheets. These amounts are offset on the consolidated balance sheets.
	The following tables (in thousands) present the Company's gross derivative financial assets and liabilities at March 31, 2015 and September 30, 2014, and the related impact of enforceable master netting arrangements and cash collateral, where applicable:
		Gross				Amount				Net Amount				Held/Pledged				Net
		Amount				Offset				Presented in				Financial				Amount
										Consolidated				Instruments1
										Balance Sheets
	March 31, 2015
	Derivative financial assets:
	Derivatives subject to master netting arrangement or similar arrangement	$	71			$	(71	)		$	—			$	—			$	—
	Derivative financial liabilities:
	Derivatives subject to master netting arrangement or similar arrangement	(48,858		)		71				(48,787		)		48,787				—
	Total derivative financial liabilities	$	(48,787	)		$	—			$	(48,787	)		$	48,787			$	—
	1 The actual amount of collateral exceeds the fair value exposure, at the individual counterparty level, as of the date presented.
		Gross				Amount				Net Amount				Held/Pledged				Net
		Amount				Offset				Presented in				Financial				Amount
										Consolidated				Instruments
										Balance Sheets
	September 30, 2014
	Derivative financial assets:
	Derivatives subject to master netting arrangement or similar arrangement	$	6,213			$	(6,213	)		$	—			$	—			$	—
	Derivative financial liabilities:
	Derivatives subject to master netting arrangement or similar arrangement	(19,286		)		6,213				(13,073		)		13,073				—
	Total derivative financial liabilities	$	(13,073	)		$	—			$	(13,073	)		$	13,073			$	—

The_Fair_Value_Option

The Fair Value Option

6 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

The Fair Value Option

The Fair Value Option

The Company has elected to measure certain long-term loans and written loan commitments at fair value to assist in managing the interest rate risk for longer-term loans. This fair value option was elected upon the origination of these loans. Interest income is recognized in the same manner as interest on non-fair value loans.

See Note 17 for additional disclosures regarding the fair value of the fair value option loans and written loan commitments.

Long-term loans and written loan commitments for which the fair value option has been elected had a net favorable difference between the aggregate fair value and the aggregate unpaid loan principal balance and written loan commitment amount of approximately $43.3 million and $7.1 million at March 31, 2015 and September 30, 2014, respectively. The total unpaid principal balance of these long-term loans was approximately $1,017.3 million and $978.3 million at March 31, 2015 and September 30, 2014, respectively. The fair value of these loans and written loan commitments is included in total loans in the consolidated balance sheets and are grouped with commercial non real estate, commercial real estate, and agricultural loans in Note 5. The fair value of these written loan commitments was not material at March 31, 2015 and September 30, 2014, respectively. None of the noted loans were greater than 90 days past due or in nonaccrual status as of March 31, 2015 or September 30, 2014.

Changes in fair value for items for which the fair value option has been elected and the line items in which these changes are reported are as follows for the three and six months ended March 31, 2015 and 2014 (in thousands):

For the Three Months Ended

For the Six Months Ended

March 31, 2015

March 31, 2014

March 31, 2015

March 31, 2014

Noninterest

Total Changes

Noninterest

Total Changes

Noninterest

Total Changes

Noninterest

Total Changes

Income

in Fair Value

Income

in Fair Value

Income

in Fair Value

Income

in Fair Value

Long-term loans and written loan commitments

$

15,208

$

15,208

$

8,730

$

8,730

$

32,308

$

32,308

$

(380

)

$

(380

)

For long-term loans and written loan commitments, $(1.2) million and $0.7 million for the three months ended March 31, 2015 and 2014, respectively, and $0.5 million and $0.7 million for the six months ended March 31, 2015 and 2014, respectively of the total change in fair value is attributable to changes in specific credit risk. The gains or losses attributable to changes in instrument-specific credit risk were determined based on an assessment of existing market conditions and credit quality of the underlying loan for the specific portfolio of loans.

Core_Deposits_and_Other_Intang

Core Deposits and Other Intangibles	6 Months Ended
	Mar. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Core Deposits and Other Intangibles	Core Deposits and Other Intangibles
	A summary of intangible assets subject to amortization is as follows (in thousands):
		Core Deposit			Brand			Customer			Total
		Intangible			Intangible			Relationships
								Intangible
	As of March 31, 2015
	Gross carrying amount	$	92,679		$	8,464		$	16,089		$	117,232
	Accumulated amortization	(90,819		)	(3,854		)	(12,956		)	(107,629		)
	Net intangible assets	$	1,860		$	4,610		$	3,133		$	9,603
	As of September 30, 2014
	Gross carrying amount	$	92,679		$	8,464		$	16,089		$	117,232
	Accumulated amortization	(87,423		)	(3,572		)	(12,008		)	(103,003		)
	Net intangible assets	$	5,256		$	4,892		$	4,081		$	14,229
	Amortization expense of intangible assets was $2.3 million and $4.7 million for the three months ended March 31, 2015 and 2014, respectively and $4.6 million and $9.4 million for the six months ended March 31, 2015 and 2014, respectively.
	The estimated amortization expense of intangible assets assumes no activities, such as acquisitions, which would result in additional amortizable intangible assets. Estimated amortization expense of intangible assets in subsequent fiscal years is as follows (in thousands):
	Remaining in 2015	$	2,484
	2016	2,822
	2017	1,097
	2018	564
	2019	564
	2020 and thereafter	2,072
		$	9,603

Securities_Sold_Under_Agreemen

Securities Sold Under Agreements to Repurchase	6 Months Ended
	Mar. 31, 2015
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Abstract]
Securities Sold Under Agreements to Repurchase	Securities Sold Under Agreements to Repurchase
	Securities sold under agreements to repurchase generally mature within one to four days from the transaction date. Securities underlying the agreements had an amortized cost of approximately $176.7 million and $190.6 million and fair value of approximately $177.2 million and $188.6 million at March 31, 2015 and September 30, 2014, respectively. The Company holds the securities under third-party safekeeping agreements.

FHLB_Advances_Related_Party_No

FHLB Advances, Related Party Notes Payable and Other Borrowings	6 Months Ended
	Mar. 31, 2015
Federal Home Loan Banks [Abstract]
FHLB Advances, Related Party Notes Payable and Other Borrowings	FHLB Advances, Related Party Notes Payable and Other Borrowings
	FHLB advances, related party notes payable, and other borrowings consist of the following at March 31, 2015 and September 30, 2014 (in thousands):
		March 31, 2015		September 30, 2014
	Subordinated capital note to NAB New York (a branch of NAB), due June 2018 (callable June 2015), interest paid quarterly based on LIBOR plus 205 basis points, unsecured	$	35,795	$	35,795
	$10,000 revolving line of credit to NAB due on demand, interest paid monthly based on LIBOR plus 125 basis points, unsecured	5,500		5,500
	Total related party notes payable	41,295		41,295
	Notes payable to Federal Home Loan Bank (FHLB), interest rates from 0.21% to 3.66% and maturity dates from April 2015 to July 2023, collateralized by real estate loans and FHLB stock, with various call dates at the option of the FHLB	475,000		575,000
	Other	19		94
	Total FHLB advances and other borrowings	475,019		575,094
		$	516,314	$	616,389
	As of March 31, 2015, based on its Federal Home Loan Bank stock holdings, the combined aggregate additional borrowing capacity of the Company with the Federal Home Loan Bank was $796.3 million.
	Principal balances of loans pledged to the Federal Home Loan Bank to collateralize notes payable totaled $2,157.1 million and $2,145.5 million at March 31, 2015 and September 30, 2014, respectively.
	As of March 31, 2015, FHLB advances, related party notes payable and other borrowings are due or callable (whichever is earlier) in subsequent fiscal years as follows (in thousands):
	Remaining in 2015	$	70,519
	2016	90,000
	2017	25,000
	2018	60,795
	2019	75,000
	2020 and thereafter	195,000
		$	516,314

Income_Taxes

Income Taxes	6 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	The provision for income taxes charged to operations consists of the following for the three and six months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Currently paid or payable
	Federal	$	10,337		$	10,994		$	24,011		$	26,960
	State	1,484			1,288			3,477			3,957
		11,821			12,282			27,488			30,917
	Deferred tax (benefit) expense	(2,101		)	2,207			(4,066		)	(1,489		)
	Income tax expense	$	9,720		$	14,489		$	23,422		$	29,428
	The income tax provision differs from the amount of income tax determined by applying the U.S. federal income tax rate to pretax income due to the following for the three and six months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Computed “expected” tax expense (35%)	$	10,305		$	14,161		$	24,445		$	29,401
	Increase (decrease) in income taxes resulting from:
	Tax exempt interest income	(1,651		)	(1,174		)	(3,216		)	(2,276		)
	State income taxes, net of federal benefit	965			837			2,260			2,572
	Other	101			665			(67		)	(269		)
	Actual tax expense	$	9,720		$	14,489		$	23,422		$	29,428
	Net deferred tax assets (liabilities) consist of the following components at March 31, 2015 and September 30, 2014 (in thousands):
		March 31, 2015			September 30, 2014
	Deferred tax assets:
	Allowance for loan losses	$	21,421		$	19,683
	Compensation	606			329
	Net operating loss carryforward	94			119
	Securities available for sale	(1,310		)	3,758
	Other real estate owned	15,462			13,721
	Core deposit intangible and other fair value adjustments	11,227			10,573
	Excess tax basis of loans acquired over carrying value	8,438			9,595
	Other	4,976			6,272
	Total deferred tax assets	60,914			64,050
	Deferred tax liabilities:
	Goodwill and other intangibles	(3,707		)	(9,099		)
	Premises and equipment	(11,037		)	(4,390		)
	Excess carrying value of FDIC indemnification asset and clawback liability	(1,557		)	(4,280		)
	Other	(912		)	(1,578		)
	Total deferred tax liabilities	(17,213		)	(19,347		)
	Net deferred tax assets	$	43,701		$	44,703
	At March 31, 2015, the Company had income tax receivable of $0.2 million from the Internal Revenue Service and at September 30, 2014, had income tax payable of $4.9 million to National Americas Investment, Inc. (included in income tax payable).
	Management has determined a valuation reserve is not required for the deferred tax assets because it is more likely than not these assets could be realized through carry back to taxable income in prior years, future reversals of existing taxable temporary differences, and future taxable income.
	Uncertain tax positions were not significant at March 31, 2015 or September 30, 2014.
	The Company is no longer subject to U.S. federal, state and local or non-U.S. income tax examinations by tax authorities for years before 2009. In July 2014, the IRS issued the final report on their examination of federal income tax returns for the periods ended September 30, 2010 and 2011.  The results of the examination did not have a material effect on our financial condition or results of operations.

ProfitSharing_Plan

Profit-Sharing Plan	6 Months Ended
	Mar. 31, 2015
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Profit-Sharing Plan	Profit-Sharing Plan
	The Company participates in a multiple employer 401(k) profit sharing plan (the Plan). All employees are eligible to participate, beginning with the first day of the month coincident with or immediately following the completion of one year of service and having reached the age of 21. In addition to employee contributions, the Company may contribute discretionary amounts for eligible participants. Contribution rates for participating employees must be equal. The Company contributed $0.5 million and $0 to the Plan for the three months ended March 31, 2015 and 2014, respectively and $1.8 million and $1.2 million for the six months ended March 31, 2015 and 2014, respectively.

StockBased_Compensation

Stock-Based Compensation	6 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-Based Compensation
	On September 26, 2014, the Board of Directors adopted, and on October 10, 2014 NAB, our controlling shareholder, approved the Great Western Bancorp, Inc. 2014 Omnibus Incentive Compensation Plan (the “2014 Plan”), the Great Western Bancorp, Inc. 2014 Non-Employee Director Plan (the “2014 Director Plan”), and the Great Western Bancorp, Inc. Executive Incentive Compensation Plan (the “Bonus Plan”), collectively ("the Plans"), which provide for the issuance of restricted share units and performance based share units to certain officers, employees and directors of the Company. The Plans were primarily established to enhance the Company’s ability to attract, retain and motivate employees. The Company’s Board of Directors, the Compensation Committee of the Board of Directors ("Compensation Committee"), or executive management upon delegation of the Compensation Committee has exclusive authority to select the employees and others, including directors, to receive the awards and to establish the terms and conditions of each award made pursuant to the Company’s stock-based compensation plans.
	Stock units issued under the Company’s restricted and performance based stock plans may not be sold or otherwise transferred until the vesting period (typically 3 years) has been met and/or performance objectives have been obtained. During the vesting periods, participants do not have voting rights and dividends are accumulated until the time upon which the award vests. Upon specified events, as defined in the Plans, stock unit awards that have not vested and/or performance hurdles that have not been met will be forfeited.
	Based on the substantive terms of each award, restricted and performance-based awards are classified as equity awards and accounted for under the Treasury method. The fair value of equity-classified awards is based on the market price of the stock on the measurement date and is amortized as compensation expense on a straight-line basis over the vesting or performance period.
	Stock based compensation is recognized based on the number of awards that are ultimately expected to vest. Forfeitures are estimated based on historical turnover experience of qualified employees. For performance-based stock awards, an estimate is made of the number of shares expected to vest as a result of actual performance against the performance targets to determine the amount of compensation expense to be recognized. The estimate is reevaluated quarterly and total compensation expense is adjusted for any change in the current period. Stock-based compensation expense is included in salaries and employee benefits expense in the consolidated statements of comprehensive income. For the three months ended March 31, 2015 and 2014, stock compensation expense was $0.2 million and $0, respectively. For the six months ended March 31, 2015 and 2014, stock compensation expense was $0.7 million and $0.0 million, respectively. Related income tax benefits recognized for the three months ended March 31, 2015 and 2014 were $0.1 million and $0, respectively and $0.3 million and $0.0 million for the six months ended March 31, 2015 and 2014, respectively.
	The following is a summary of the Plans’ restricted share and performance-based stock award activity as of March 31, 2015:
	Restricted Shares	Common Shares		Weighted-Average
				Grant Date
				Fair Value
	Restricted shares, October 1, 2014	—		$	—
	Granted	79,728		18.05
	Vested and issued	—		—
	Forfeited	(556	)	18
	Canceled	—		—
	Restricted shares, March 31, 2015	79,172		$	18.05
	Vested, but not issuable at March 31, 2015	12,221		$	18
	Performance Shares
	Performance shares, October 1, 2014	—		$	—
	Granted	221,184		18
	Vested and issued	—		—
	Forfeited	(4,736	)	18
	Canceled	—		—
	Performance shares, March 31, 2015	216,448		$	18
	The number of performance shares granted is reflected in the above table at the 100% target performance level. The actual performance-based award payouts will vary based on the achievement of the pre-established targets and can range from 0% to 150% of the target amount. The outstanding number of performance shares reflected in the table represents the number of shares expected to be awarded based on estimated achievement of the goals as of year end. However, at March 31, 2015, the maximum number of performance-based shares that could be issued if performance is attained at 150% of target based on the grants made to date was approximately 324,672 shares.
	As of March 31, 2015, there was $2.5 million of unrecognized compensation cost related to nonvested restricted stock awards expected to be recognized over a period of 2.50 years.

Fair_Value_of_Financial_Instru

Fair Value of Financial Instruments and Interest Rate Risk	6 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments and Interest Rate Risk	Fair Value of Financial Instruments and Interest Rate Risk
	The Company measures, monitors and discloses certain of its assets and liabilities on a fair value basis. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value guidance also establishes a fair value hierarchy that requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The guidance describes three levels of inputs that may be used to measure fair value are as follows:
	Level 1    Quoted prices in active markets for identical assets or liabilities
	Level 2	Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities
	Level 3	Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities
	Level 1 inputs are considered to be the most transparent and reliable and Level 3 inputs are considered to be the least transparent and reliable. The Company assumes the use of the principal market to conduct a transaction of each particular asset or liability being measured and then considers the assumptions that market participants would use when pricing the asset or liability. Whenever possible, the Company first looks for quoted prices for identical assets or liabilities in active markets (Level 1 inputs) to value each asset or liability. However, when inputs from identical assets or liabilities on active markets are not available, the Company utilizes market observable data for similar assets and liabilities. The Company maximizes the use of observable inputs and limits the use of unobservable inputs to occasions when observable inputs are not available. The need to use unobservable inputs generally results from the lack of market liquidity of the actual financial instrument or of the underlying collateral. Although in some instances, third party price indications may be available, limited trading activity can challenge the observability of these quotations.
	Assets and Liabilities Measured at Fair Value on a Recurring Basis
	Following is a description of the valuation methodologies and inputs used for assets and liabilities measured at fair value on a recurring basis and recognized in the accompanying consolidated balance sheets, as well as the general classification of such assets and liabilities pursuant to the valuation hierarchy.
	Securities Available for Sale
	Where quoted market prices are available in an active market, securities are classified within Level 1 of the valuation hierarchy. Level 1 securities include U.S. Treasury securities. If quoted market prices are not available, then fair values are estimated by using pricing models, quoted prices of securities with similar characteristics, or discounted cash flows and classified as Level 2 securities. Level 2 securities include U.S. government agency, agency mortgage-backed, states and political subdivisions, corporate debt, and other securities. Where Level 1 or Level 2 inputs are not available, securities are classified within Level 3 of the hierarchy.
	Interest Rate Swaps and Loans
	Interest rate swaps are valued using the system used to value all of NAB’s traded securities and derivatives using LIBOR rates. The fair value of loans accounted for under the fair value option represents the net carrying value of the loan, plus the equal and opposite amount of the value of the swap needed to hedge the interest rate risk and an adjustment for credit risk based on our assessment of existing market conditions for the specific portfolio of loans. This is used due to the strict prepayment penalties put in the loan terms to cover the cost of exiting the hedge of the loans in the case of early prepayment or termination. The adjustment for credit risk on loans accounted for under the fair value option is not significant to the overall fair value of the loans. The fair values estimated by NAB use interest rates that are observable or that can be corroborated by observable market data and, therefore, are classified within Level 2 of the valuation hierarchy. The Company is required to post cash collateral to NAB for interest rate derivative contracts that are in a liability position, thus a credit risk adjustment on interest rate swaps is not warranted.
	The following table presents the fair value measurements of assets and liabilities recognized in the accompanying consolidated balance sheets measured at fair value on a recurring basis and the level within the fair value hierarchy in which the fair value measurements fall at March 31, 2015 and September 30, 2014 (in thousands):
		Fair Value				Level 1				Level 2				Level 3
	As of March 31, 2015
	U.S. Treasury securities	$	275,477			$	275,477			$	—			$	—
	U.S. Agency securities	74,801				—				74,801				—
	Mortgage-backed securities	1,044,021				—				1,044,021				—
	States and political subdivision securities	2,108				—				150				1,958
	Corporate debt securities	5,062				—				5,062				—
	Other	1,039				—				1,039				—
	Securities available for sale	$	1,402,508			$	275,477			$	1,125,073			$	1,958
	Derivatives-assets	$	27			$	—			$	27			$	—
	Derivatives-liabilities	48,814				—				48,814				—
	Fair value loans and written loan	1,060,598				—				1,060,598				—
	commitments
		Fair Value				Level 1				Level 2				Level 3
	As of September 30, 2014
	U.S. Treasury securities	$	222,725			$	222,725			$	—			$	—
	U.S. Agency securities	—				—				—				—
	Mortgage-backed securities	1,103,415				—				1,103,415				—
	States and political subdivision securities	2,189				—				160				2,029
	Corporate debt securities	11,873				—				11,873				—
	Other	1,040				—				1,040				—
	Securities available for sale	$	1,341,242			$	222,725			$	1,116,488			$	2,029
	Derivatives-assets	$	19			$	—			$	19			$	—
	Derivatives-liabilities	13,092				—				13,092				—
	Fair value loans and written loan	985,411				—				985,411				—
	commitments
	The following table presents the changes in Level 3 financial instruments for the three months ended March 31, 2015 and 2014 (in thousands):
		Other Securities Available for Sale
	Balance as of December 31, 2014	$	1,958
	Principal paydown	—
	Balance as of March 31, 2015	$	1,958
	Balance as of December 31, 2013	$	2,243
	Principal paydown	—
	Balance as of March 31, 2014	$	2,243
	The following table presents the changes in Level 3 financial instruments for the six months ended March 31, 2015 and 2014 (in thousands):
		Other Securities Available for Sale
	Balance as of September 30, 2014	$	2,029
	Principal paydown	(71		)
	Balance as of March 31, 2015	$	1,958
	Balance as of September 30, 2013	$	2,243
	Principal paydown	—
	Balance as of March 31, 2014	$	2,243
	Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
	Following is a description of the valuation methodologies used for assets and liabilities measured at fair value on a nonrecurring basis and recognized in the accompanying consolidated balance sheets, as well as the general classification of such assets and liabilities pursuant to the valuation hierarchy.
	Impaired Loans (Collateral Dependent)
	Loans for which it is probable that the Company will not collect all principal and interest due according to contractual terms are measured for impairment. Allowable methods for estimating fair value include using the fair value of the collateral for collateral dependent loans or, where a loan is determined not to be collateral dependent, using the discounted cash flow method.
	If the impaired loan is identified as collateral dependent, then the fair value method of measuring the amount of the impairment is utilized. This method requires obtaining a current independent appraisal of the collateral and applying a discount factor, if necessary, to the appraised value and including costs to sell. Because many of these inputs are not observable, the measurements are classified as Level 3.
	Other Real Estate Owned (OREO)
	Other real estate owned consists of loan collateral that has been repossessed through foreclosure. This collateral is comprised of commercial and residential real estate. OREO is recorded initially at fair value of the collateral less estimated selling costs. Subsequent to foreclosure, valuations are updated periodically, and the assets may be marked down further to fair value less selling costs, reflecting a valuation allowance. Fair value measurements may be based upon appraisals, third-party price opinions, or internally developed pricing methods. These measurements are classified as Level 3.
	Mortgage Loans Held for Sale
	Fair value of mortgage loans held for sale is based on either quoted prices for the same or similar loans, or values obtained from third parties, or are estimated for portfolios of loans with similar financial characteristics and are therefore considered a Level 2 valuation.
The following tables present the fair value measurement of assets and liabilities measured at fair value on a nonrecurring basis and the level within the fair value hierarchy in which the fair value measurements fall at March 31, 2015 and September 30, 2014 (in thousands):
	Fair Value				Level 1				Level 2				Level 3
As of March 31, 2015
Other real estate owned	$	25,162			$	—			$	—			$	25,162
Impaired loans	161,904				—				—				161,904
Loans held for sale, at lower of cost or fair	9,006				—				9,006				—
value
As of September 30, 2014
Other real estate owned	$	36,879			$	—			$	—			$	36,879
Impaired loans	111,265				—				—				111,265
Loans held for sale, at lower of cost or fair	10,381				—				10,381				—
value
The valuation techniques and significant unobservable inputs used to measure Level 3 fair value measurements at March 31, 2015 were as follows (in thousands):
Financial	Fair Value of Assets / (Liabilities) at March 31, 2015				Valuation		Unobservable		Range		Weighted
Instrument					Technique(s)		Input				Average
Other real estate	$	25,162			Appraisal value		Property specific adjustment		N/A		N/A
owned
Impaired loans	$	161,904			Appraisal value		Property		N/A		N/A
							specific adjustment
Fair Value of Financial Instruments
For financial instruments that have quoted market prices, those quotes are used to determine fair value. Financial instruments that have no defined maturity, have a remaining maturity of 180 days or less, or reprice frequently to a market rate are assumed to have a fair value that approximates carrying value, after taking into consideration any applicable credit risk. If no market quotes are available, financial instruments are valued by discounting the expected cash flows using an estimated current market interest rate for the financial instrument.
The short maturity of the Company’s assets and liabilities results in having a significant number of financial instruments whose fair value equals or closely approximates carrying value. Such financial instruments are reported in the following consolidated balance sheet categories: cash and due from banks, securities sold under agreements to repurchase, and accrued interest.
Fair value estimates are based on existing on and off-balance sheet financial instruments without attempting to estimate the value of anticipated future business and the value of assets and liabilities that are not considered financial instruments. Significant assets and liabilities that are not considered financial instruments include premises and equipment, deferred income taxes, goodwill, and core deposit and other intangibles. In addition, the tax ramifications related to the realization of unrealized gains and losses can have a significant effect on fair value estimates and have not been considered in the estimates.
Off-balance sheet instruments (commitments to extend credit and standby letters of credit) are generally short-term and at variable rates. Therefore, both the carrying amount and the estimated fair value associated with these instruments are immaterial. Fair values for balance sheet instruments as of March 31, 2015 and September 30, 2014, are as follows (in thousands):
			March 31, 2015								September 30, 2014
	Level in		Carrying				Fair Value				Carrying				Fair Value
	Fair Value		Amount								Amount
	Hierarchy
Assets
Cash and due from banks	Level 1		$	358,440			$	358,440			$	256,639			$	256,639
Loans, net excluding fair valued loans and loans	Level 3		5,950,437				5,935,242				5,744,157				5,734,274
held for sale
Accrued interest receivable	Level 2		37,933				37,933				42,609				42,609
Federal Home Loan Bank stock	Level 2		31,810				31,810				35,922				35,922
Liabilities
Deposits	Level 3		$	7,487,698			$	7,499,432			$	7,052,180			$	7,057,591
FHLB advances, related party notes payable, and other borrowings	Level 2		516,314				510,339				616,389				604,615
Securities sold under repurchase agreements	Level 2		163,343				163,343				161,687				161,687
Accrued interest payable	Level 2		4,469				4,469				5,273				5,273
Subordinated debentures	Level 2		56,083				56,084				56,083				56,084
The following methods and assumptions were used in estimating the fair value of financial instruments that were not previously disclosed:
Cash and cash due from banks: Due to the short term nature of cash and cash equivalents, the estimated fair value is equal to the carrying value and they are categorized as a Level 1 fair value measurement.
Loans, net excluding fair valued loans and loans held for sale: The fair value of the loan portfolio is estimated using observable inputs including estimated cash flows, and discount rates based on interest rates currently being offered for loans with similar terms, to borrowers of similar credit quality. Loans held for investment are categorized as a Level 3 fair value measurement.
Accrued interest receivable: Due to the nature of accrued interest receivable, the estimated fair value is equal to the carrying value and they are categorized as a Level 2 fair value measurement.
Federal Home Loan Bank stock: The carrying amount of FHLB stock approximates its fair value as it can only be redeemed with the FHLB at par value. Federal Home Loan Bank stock has been categorized as a Level 2 fair value measurement.
Deposits: The estimated fair value of deposits with no stated maturity, such as non-interest bearing demand deposits, savings, NOW, and money market accounts, is equal to the amount payable on demand. The fair value of interest-bearing time deposits is based on the discounted value of contractual cash flows of such deposits, taking into account the option for early withdrawal. The discount rate is estimated using the rates offered by the Company, at the respective measurement dates, for deposits of similar maturities. Deposits have been categorized as a Level 3 fair value measurement.
FHLB advances, related party notes payable, and other borrowings: The fair value of FHLB advances, related party notes payable, and other borrowings is estimated using discounted cash flow analysis, based on current incremental borrowing rates for similar types of borrowing arrangements. In the absence of a reasonably precise methodology to determine the fair value of the credit agreement, carrying value has been used to represent fair value. FHLB advances, related party notes payable, and other borrowings have been categorized as a Level 2 fair value measurement.
Securities sold under repurchase agreements: The Company’s repurchase agreements are overnight transactions that mature the day after the transaction, and as a result of this short-term nature, the estimated fair value equals the carrying value. Securities sold under repurchase agreements have been categorized as a Level 2 fair value measurement.
Accrued interest payable: Due to the nature of accrued interest payable, the estimated fair value is equal to the carrying value and they are categorized as a Level 2 fair value measurement.
Subordinated Debentures: The fair value of subordinated debentures is estimated using discounted cash flow analysis, based on current incremental debt rates. Subordinated debentures have been categorized as a Level 2 fair value measurement.

Earnings_per_Share

Earnings per Share	6 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings per Share	Earnings per Share
	Basic earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period, excluding outstanding non-vested restricted stock awards. Diluted earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding determined for the basic earnings per share calculation plus the dilutive effect of stock compensation using the treasury stock method.
	The following information was used in the computation of basic earnings per share (EPS) for the three and six months ended March 31, 2015 and 2014 (in thousands except share data).
		Three Months Ended				Six Months Ended
		March 31,				March 31,
		2015		2014		2015		2014
	Net income	$	19,724	$	25,971	$	46,421	$	54,575
	Weighted average common shares outstanding	57,898,335		57,886,114		57,897,059		57,886,114
	Dilutive effect of stock based compensation	18,467		—		9,234		—
	Weighted average common shares outstanding for diluted earnings per share calculation	57,916,802		57,886,114		57,906,293		57,886,114
	Basic earnings per share	$	0.34	$	0.45	$	0.8	$	0.94
	Diluted earnings per share	$	0.34	$	0.45	$	0.8	$	0.94
	The Company had 216,448 and 0 shares of unvested performance stock as of March 31, 2015 and 2014, respectively, that were not included in the computation of diluted earnings per common share because performance conditions for vesting had not been met. The Company had 1,665 and 0 shares of anti-dilutive stock awards outstanding as of March 31, 2015 and 2014, respectively.

Basis_of_Presentation_Tables

Basis of Presentation (Tables)	6 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Error Corrections and Prior Period Adjustments	The following table reflects the impact of the matter described above on previously filed financial statements:
		Previously Reported			Currently Reported
		Interest Income			Noninterest Income
	Six months ended March 31, 2014
	Realized gain on derivatives	$	(8,678	)	$	(8,678	)
	Six months ended March 31, 2013
	Realized gain (loss) on derivatives	$	(6,668	)	$	(6,668	)
	Twelve months ended September 30, 2014
	Realized gain (loss) on derivatives	$	(18,255	)	$	(18,255	)
	Twelve months ended September 30, 2013
	Realized gain (loss) on derivatives	$	(14,217	)	$	(14,217	)
	Twelve months ended September 30, 2012
	Realized gain (loss) on derivatives	$	(9,931	)	$	(9,931	)
	The following table reflects the impact of the matter described above on previously filed financial statements:
		Previously Reported						Currently Reported
		Interest Income			Noninterest Expense			Noninterest Income
	Six months ended March 31, 2014
	Unrealized gain (loss) on derivatives	$	—		$	(1,078	)	$	—		$	(1,078	)
	Loan fair value change related to interest rates	1,078			—			1,078			—
	Loan fair value change related to credit quality	(698		)	—			(698		)	—
		$	380		$	(1,078	)	$	380		$	(1,078	)
	Six months ended March 31, 2013
	Unrealized gain (loss) on derivatives	$	—		$	(14,124	)	$	—		$	(14,124	)
	Loan fair value change related to interest rates	14,124			—			14,124			—
	Loan fair value change related to credit quality	(396		)	—			(396		)	—
		$	13,728		$	(14,124	)	$	13,728		$	(14,124	)
	Twelve months ended September 30, 2014
	Unrealized gain (loss) on derivatives	$	—		$	11,922		$	—		$	11,922
	Loan fair value change related to interest rates	(11,922		)	—			(11,922		)	—
	Loan fair value change related to credit quality	18			—			18			—
		$	(11,904	)	$	11,922		$	(11,904	)	$	11,922
	Twelve months ended September 30, 2013
	Unrealized gain (loss) on derivatives	$	—		$	(40,305	)	$	—		$	(40,305	)
	Loan fair value change related to interest rates	40,305			—			40,305			—
	Loan fair value change related to credit quality	855			—			855			—
		$	41,160		$	(40,305	)	$	41,160		$	(40,305	)
	Twelve months ended September 30, 2012
	Unrealized gain (loss) on derivatives	$	—		$	19,369		$	—		$	19,369
	Loan fair value change related to interest rates	(19,369		)	—			(19,369		)	—
	Loan fair value change related to credit quality	4,276			—			4,276			—
		$	(15,093	)	$	19,369		$	(15,093	)	$	19,369

Securities_Available_for_Sale_

Securities Available for Sale (Tables)	6 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Amortized Cost and Fair Value	The amortized cost and approximate fair value of investments in securities, all of which are classified as available for sale according to management’s intent, are summarized as follows (in thousands):
		Amortized			Gross			Gross			Fair Value
					Unrealized			Unrealized
					Gains			Losses
	As of March 31, 2015
	U.S. Treasury securities	$	271,753		$	3,724		$	—		$	275,477
	U.S. Agency securities	74,345			456			—			74,801
	Mortgage-backed securities:
	Government National Mortgage Association	945,299			4,266			(4,469		)	945,096
	Federal National Mortgage Association	48,495			—			(129		)	48,366
	Small Business Assistance Program	51,086			—			(527		)	50,559
	States and political subdivision securities	2,107			1			—			2,108
	Corporate debt securities	4,996			66			—			5,062
	Other	1,006			33			—			1,039
		$	1,399,087		$	8,546		$	(5,125	)	$	1,402,508
		Amortized			Gross			Gross			Fair Value
					Unrealized			Unrealized
					Gains			Losses
	As of September 30, 2014
	U.S. Treasury securities	$	222,868		$	31		$	(174	)	$	222,725
	U.S. Agency securities	—			—			—			—
	Mortgage-backed securities:
	Government National Mortgage Association	1,113,363			4,639			(14,587		)	1,103,415
	Federal National Mortgage Association	—			—			—			—
	Small Business Assistance Program	—			—			—			—
	States and political subdivision securities	2,188			1			—			2,189
	Corporate debt securities	11,732			141			—			11,873
	Other	1,006			34			—			1,040
		$	1,351,157		$	4,846		$	(14,761	)	$	1,341,242
Marketable Securities	The amortized cost and approximate fair value of debt securities available for sale as of March 31, 2015 and September 30, 2014, by contractual maturity, are shown below. Maturities of mortgage-backed securities may differ from contractual maturities because the mortgages underlying the securities may be called or repaid without any penalties.
		31-Mar-15						30-Sep-14
	(In Thousands)	Amortized Cost			Fair Value			Amortized Cost			Fair Value
	Due in one year or less	$	76,162		$	76,620		$	7,207		$	7,218
	Due after one year through five years	272,043			275,766			223,282			223,140
	Due after five years through ten years	4,996			5,062			6,299			6,429
		353,201			357,448			236,788			236,787
	Mortgage-backed securities	1,044,880			1,044,021			1,113,363			1,103,415
	Securities without contractual maturities	1,006			1,039			1,006			1,040
		$	1,399,087		$	1,402,508		$	1,351,157		$	1,341,242
Schedule of Unrealized Loss on Investments	The following table presents the Company’s gross unrealized losses and approximate fair value in investments, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position (in thousands):
		Less than 12 months						March 31, 2015						Total
								12 months or more
		Fair Value			Unrealized			Fair Value			Unrealized			Fair Value		Unrealized
	U.S. Treasury securities	$	—		$	—		$	—		$	—		$	—	$	—
	U. S. Agency securities	—			—			—			—			$	—	$	—
	Mortgage-backed securities	83,704			(656		)	479,290			(4,469		)	562,994		(5,125		)
	Corporate debt securities	—			—			—			—			—		—
	Other	—			—			—			—			—		—
		$	83,704		$	(656	)	$	479,290		$	(4,469	)	$	562,994	$	(5,125	)
		Less than 12 months						September 30, 2014						Total
								12 months or more
		Fair Value			Unrealized			Fair Value			Unrealized			Fair Value		Unrealized
	U.S. Treasury securities	$	98,344		$	(174	)	$	—		$	—		$	98,344	$	(174	)
	U.S. Agency securities	—			—			—			—			$	—	$	—
	Mortgage-backed securities	24,625			(125		)	730,171			(14,462		)	754,796		(14,587		)
	Corporate debt securities	—			—			—			—			—		—
	Other	—			—			—			—			—		—
		$	122,969		$	(299	)	$	730,171		$	(14,462	)	$	853,140	$	(14,761	)
Unrealized Gain (Loss) on Investments	The components of other comprehensive income from net unrealized gains (losses) on securities available for sale for the three and six months ended March 31, 2015 and 2014, respectively are as follows (in thousands):
		Three Months Ended						Six Months Ended March 31,
		March 31,
		2015			2014			2015			2014
	Beginning balance accumulated other comprehensive income (loss)	$	(3,042	)	$	(13,535	)	$	(6,157	)	$	(7,081	)
	Net unrealized holding gain (loss) arising during the period	8,312			10,020			13,285			(389		)
	Reclassification adjustment for net gain realized in net income	—			(6		)	(51		)	(6		)
	Net change in unrealized gain (loss) before income taxes	8,312			10,014			13,234			(395		)
	Income tax (expense) benefit	(3,159		)	(3,693		)	(4,966		)	262
	Net change in unrealized gain (loss) on securities after taxes	5,153			6,321			8,268			(133		)
	Ending balance accumulated other comprehensive income (loss)	$	2,111		$	(7,214	)	$	2,111		$	(7,214	)

Loans_Tables

Loans (Tables)	6 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Schedule of Loans Receivable	The composition of net loans as of March 31, 2015 and September 30, 2014, is as follows (in thousands):
		March 31, 2015				September 30, 2014
	Residential real estate	$	905,114			$	901,605
	Commercial real estate	2,673,255				2,541,194
	Commercial non real estate	1,657,856				1,571,640
	Agriculture	1,748,366				1,681,209
	Consumer	80,036				90,086
	Other	35,433				34,243
		7,100,060				6,819,977
	Less:
	Allowance for loan losses	(52,426		)		(47,518		)
	Unamortized discount on acquired loans	(21,774		)		(25,638		)
	Unearned net deferred fees and costs and loans in process	(5,821		)		(6,872		)
		$	7,020,039			$	6,739,949
Schedule of Company's Nonaccrual Loans	The following table presents the Company’s nonaccrual loans at March 31, 2015 and September 30, 2014 (in thousands), excluding loans covered under the FDIC loss-sharing agreements. Loans greater than 90 days past due and still accruing interest as of March 31, 2015 and September 30, 2014, were not significant.
	Nonaccrual loans	March 31, 2015				September 30, 2014
	Residential real estate	$	7,690			$	6,671
	Commercial real estate	10,836				20,767
	Commercial non real estate	9,015				4,908
	Agriculture	18,860				11,453
	Consumer	111				146
	Total	$	46,512			$	43,945
Past Due Financing Receivables	The following table (in thousands) presents the Company’s past due loans at March 31, 2015 and September 30, 2014. This table is presented net of unamortized discount on acquired loans and excludes loans measured at fair value with changes in fair value reported in earnings of $1,060.6 million for March 31, 2015 and $985.4 million for September 30, 2014.
	As of March 31, 2015	30-59 Days				60-89 Days				Greater Than				Total				Current				Total
		Past Due				Past Due				90 Days				Past Due								Financing
																						Receivables
	Residential real estate	$	1,909			$	562			$	2,854			$	5,325			$	777,219			$	782,544
	Commercial real estate	165				2,316				4,816				7,297				2,284,882				2,292,179
	Commercial non real estate	3,344				622				4,262				8,228				1,221,359				1,229,587
	Agriculture	3,491				—				834				4,325				1,406,083				1,410,408
	Consumer	218				28				35				281				79,603				79,884
	Other	—				—				—				—				35,433				35,433
		9,127				3,528				12,801				25,456				5,804,579				5,830,035
	Loans covered by FDIC loss sharing agreements	4,744				214				2,768				7,726				179,923				187,649
	Total	$	13,871			$	3,742			$	15,569			$	33,182			$	5,984,502			$	6,017,684
	As of September 30, 2014	30-59 Days				60-89 Days				90 Days or Greater Past Due				Total				Current				Total
		Past Due				Past Due								Past Due								Financing
																						Receivables
	Residential real estate	$	675			$	611			$	2,581			$	3,867			$	760,887			$	764,754
	Commercial real estate	11,050				819				3,384				15,253				1,988,585				2,003,838
	Commercial non real estate	1,761				6,228				744				8,733				1,303,925				1,312,658
	Agriculture	16				368				4,205				4,589				1,364,960				1,369,549
	Consumer	244				18				49				311				89,528				89,839
	Other	—				—				—				—				34,243				34,243
		13,746				8,044				10,963				32,753				5,542,128				5,574,881
	Loans covered by FDIC loss sharing agreements	1,960				1,252				3,728				6,940				227,096				234,036
	Total	$	15,706			$	9,296			$	14,691			$	39,693			$	5,769,224			$	5,808,917
Composition of Loan Portfolio by Internal Risk Rating	The composition of the loan portfolio by internally assigned grade is as follows as of March 31, 2015 and September 30, 2014. This table (in thousands) is presented net of unamortized discount on acquired loans and excludes loans measured at fair value with changes in fair value reported in earnings of $1,060.6 million for March 31, 2015 and $985.4 million for September 30, 2014:
	As of March 31, 2015	Residential				Commercial				Commercial				Agriculture				Consumer				Other		Total
		Real Estate				Real Estate				Non Real
										Estate
	Credit Risk Profile by Internally Assigned Grade
	Grade:
	Pass	$	765,058			$	2,122,618			$	1,093,867			$	1,188,111			$	79,244			$	35,433	$	5,284,331
	Watchlist	5,248				105,838				96,724				176,266				372				—		384,448
	Substandard	11,759				63,540				36,627				44,290				259				—		156,475
	Doubtful	428				183				2,369				1,741				1				—		4,722
	Loss	51				—				—				—				8				—		59
	Ending balance	782,544				2,292,179				1,229,587				1,410,408				79,884				35,433		5,830,035
	Loans covered by FDIC loss sharing agreements	113,578				63,268				8,925				1,832				46				—		187,649
	Total	$	896,122			$	2,355,447			$	1,238,512			$	1,412,240			$	79,930			$	35,433	$	6,017,684
	As of September 30, 2014	Residential				Commercial				Commercial				Agriculture				Consumer				Other		Total
		Real Estate				Real Estate				Non Real
										Estate
	Credit Risk Profile by Internally Assigned Grade
	Grade:
	Pass	$	747,485			$	1,867,866			$	1,218,558			$	1,202,145			$	89,197			$	34,243	$	5,159,494
	Watchlist	5,320				84,132				65,628				132,262				381				—		287,723
	Substandard	11,290				51,692				27,499				35,107				242				—		125,830
	Doubtful	659				148				798				35				19				—		1,659
	Loss	—				—				175				—				—				—		175
	Ending balance	764,754				2,003,838				1,312,658				1,369,549				89,839				34,243		5,574,881
	Loans covered by FDIC loss sharing agreements	127,115				95,467				9,390				2,004				60				—		234,036
	Total	$	891,869			$	2,099,305			$	1,322,048			$	1,371,553			$	89,899			$	34,243	$	5,808,917
Impaired Financing Receivables	The following table presents the Company’s impaired loans (in thousands). This table excludes loans covered by FDIC loss sharing agreements:
		Recorded				Unpaid				Related				Average
		Investment				Principal				Allowance				Recorded
						Balance								Investment
	As of March 31, 2015
	Impaired loans:
	With an allowance recorded:
	Residential real estate	$	12,332			$	12,452			$	2,721			$	12,220
	Commercial real estate	73,729				75,381				1,753				67,942
	Commercial non real estate	41,310				49,834				6,905				36,916
	Agriculture	46,031				46,059				3,007				40,780
	Consumer	268				325				52				274
		$	173,670			$	184,051			$	14,438			$	158,132
		Recorded				Unpaid				Related				Average
		Investment				Principal				Allowance				Recorded
						Balance								Investment
	As of September 30, 2014
	Impaired loans:
	With an allowance recorded:
	Residential real estate	$	12,107			$	12,737			$	2,529			$	13,572
	Commercial real estate	62,155				64,597				2,017				84,490
	Commercial non real estate	32,522				37,882				3,927				31,827
	Agriculture	35,528				37,958				1,155				30,546
	Consumer	280				491				51				346
		$	142,592			$	153,665			$	9,679			$	160,781
	The following table provides purchased impaired loans at March 31, 2015 and September 30, 2014 (in thousands):
		March 31, 2015												30-Sep-14
		Outstanding				Recorded				Carrying				Outstanding				Recorded				Carrying
		Balance 1				Investment 2				Value 3				Balance 1				Investment 2				Value 3
	Residential real estate	$	110,499			$	93,277			$	91,143			$	115,863			$	102,987			$	100,203
	Commercial real estate	107,514				27,835				27,126				130,825				49,202				48,557
	Commercial non real estate	14,710				5,348				5,348				16,697				6,361				6,361
	Agriculture	1,623				1,595				1,595				1,747				1,746				1,746
	Consumer	1,838				1,466				1,466				2,019				1,843				1,818
	Total lending	$	236,184			$	129,521			$	126,678			$	267,151			$	162,139			$	158,685
	1    Represents the legal balance of loans acquired with deteriorated credit quality.
	2    Represents the book balance of loans acquired with deteriorated credit quality.
	3    Represents the book balance of loans acquired with deteriorated credit quality net of the related allowance for loan losses.
Troubled Debt Restructurings on Financing Receivables	The following table presents the recorded value of the Company’s TDR balances as of March 31, 2015 and September 30, 2014 (in thousands):
		31-Mar-15								30-Sep-14
		Accruing				Nonaccrual				Accruing				Nonaccrual
	Residential real estate	$	618			$	1,929			$	1,112			$	1,730
	Commercial real estate	45,160				5,424				25,177				6,884
	Commercial non real estate	10,165				1,445				6,753				1,785
	Agriculture	2,159				6,377				3,780				9,994
	Consumer	20				13				35				22
	Total	$	58,122			$	15,188			$	36,857			$	20,415
	The following table presents a summary of all accruing loans restructured in TDRs during the three months ended March 31, 2015 and 2014, respectively:
		Three Months Ended March 31,
		2015											2014
					Recorded Investment											Recorded Investment
	($ in thousands)	Number			Pre-				Post-				Number			Pre-				Post-
					Modification				Modification							Modification				Modification
	Residential real estate
	Rate modification	1			$	15			$	15			—			$	—			$	—
	Term extension	—			—				—				—			—				—
	Payment modification	—			—				—				—			—				—
	Bankruptcy	—			—				—				—			—				—
	Other	1			21				21				—			—				—
	Total residential real estate	2			36				36				—			—				—
	Commercial real estate
	Rate modification	—			—				—				—			—				—
	Term extension	1			90				—				—			—				—
	Payment modification	4			3,660				3,660				—			—				—
	Bankruptcy	1			498				498				—			—				—
	Other	—			—				—				—			—				—
	Total commercial real estate	6			4,248				4,158				—			—				—
	Commercial non real estate
	Rate modification	—			—				—				—			—				—
	Term extension	3			2,879				2,879				1			35				35
	Payment modification	1			50				50				2			67				67
	Bankruptcy	—			—				—				—			—				—
	Other	—			—				—				1			327				327
	Total commercial non real estate	4			2,929				2,929				4			429				429
	Agriculture
	Rate modification	—			—				—				—			—				—
	Term extension	—			—				—				—			—				—
	Payment modification	—			—				—				—			—				—
	Bankruptcy	—			—				—				—			—				—
	Other	—			—				—				—			—				—
	Total agriculture	—			—				—				—			—				—
	Consumer
	Rate modification	—			—				—				—			—				—
	Term extension	—			—				—				—			—				—
	Payment modification	—			—				—				2			4				4
	Bankruptcy	1			6				6				—			—				—
	Other	—			—				—				1			18				18
	Total consumer	1			6				6				3			22				22
	Total accruing	13			$	7,219			$	7,129			7			$	451			$	451
	Change in recorded investment due to principal paydown at time of modification	—			—								—			—				—
	Change in recorded investment due to chargeoffs at time of modification	1			90				—				—			—				—
	The following table presents a summary of all accruing loans restructured in TDRs during the six months ended March 31, 2015 and 2014:
		Six Months Ended March 31,
		2015											2014
					Recorded Investment											Recorded Investment
	($ in thousands)	Number			Pre-				Post-				Number			Pre-				Post-
					Modification				Modification							Modification				Modification
	Residential real estate
	Rate modification	1			$	15			$	15			—			$	—			$	—
	Term extension	—			—				—				2			74				74
	Payment modification	—			—				—				1			15				15
	Bankruptcy	—			—				—				1			130				130
Other	1			21				21				—			—				—
Total residential real estate	2			36				36				4			219				219
Commercial real estate
Rate modification	—			—				—				—			—				—
Term extension	1			90				—				—			—				—
Payment modification	6			22,542				22,542				1			1,070				1,070
Bankruptcy	1			498				498				—			—				—
Other	—			—				—				—			—				—
Total commercial real estate	8			23,130				23,040				1			1,070				1,070
Commercial non real estate
Rate modification	1			32				32				—			—				—
Term extension	3			2,879				2,879				4			1,734				1,734
Payment modification	2			1,874				1,874				4			735				735
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				1			327				327
Total commercial non real estate	6			4,785				4,785				9			2,796				2,796
Agriculture
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				—			—				—
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				—			—				—
Total agriculture	—			—				—				—			—				—
Consumer
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				—			—				—
Payment modification	—			—				—				2			4				4
Bankruptcy	1			6				6				—			—				—
Other	—			—				—				2			28				28
Total consumer	1			6				6				4			32				32
Total accruing	17			27,957				27,867				18			$	4,117			$	4,117
Change in recorded investment due to principal paydown at time of modification	—			—								—			—				—
Change in recorded investment due to chargeoffs at time of modification	1			90				—				—			—				—
The following table presents a summary of all non-accruing loans restructured in TDRs during the three months ended March 31, 2015 and 2014:
	Three Months Ended March 31,
	2015											2014
				Recorded Investment											Recorded Investment
($ in thousands)	Number			Pre-				Post-				Number			Pre-				Post-
				Modification				Modification							Modification				Modification
Residential real estate
Rate modification	2			$	104			$	104			4			$	98			$	98
Term extension	1			77				77				1			15				15
Payment modification	—			—				—				—			—				—
Bankruptcy	1			43				43				—			—				—
Other	—			—				—				—			—				—
Total residential real estate	4			224				224				5			113				113
Commercial real estate
Rate modification	—			—				—				2			500				500
Term extension	—			—				—				2			4,031				4,031
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				1			87				87
Total commercial real estate	—			—				—				5			4,618				4,618
Commercial Non Real Estate
Rate modification	—			—				—				—			—				—
Term extension	4			217				217				—			—				—
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				1			10				10
Other	—			—				—				—			—				—
Total commercial non real estate	4			217				217				1			10				10
Agriculture
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				2			260				260
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				—			—				—
Total agriculture	—			—				—				2			260				260
Consumer
Rate modification	—			—				—				—			—				—
Term extension	1			1				1				—			—				—
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				—			—				—
Total consumer	1			1				1				—			—				—
Total non-accruing	9			$	442			$	442			13			$	5,001			$	5,001
Change in recorded investment due to principal paydown at time of modification	—			—				—				—			—				—
Change in recorded investment due to chargeoffs at time of modification	—			—				—				—			—				—
The following table presents a summary of all non-accruing loans restructured in TDRs during the six months ended March 31, 2015 and 2014:
	Six Months Ended March 31,
	2015											2014
				Recorded Investment											Recorded Investment
($ in thousands)	Number			Pre-				Post-				Number			Pre-				Post-
				Modification				Modification							Modification				Modification
Residential real estate
Rate modification	2			$	104			$	104			4			$	98			$	98
Term extension	1			77				77				2			18				18
Payment modification	—			—				—				—			—				—
Bankruptcy	1			43				43				1			4				4
Other	—			—				—				1			38				38
Total residential real estate	4			224				224				8			158				158
Commercial real estate
Rate modification	—			—				—				2			500				500
Term extension	—			—				—				2			4,031				4,031
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				1			87				87
Total commercial real estate	—			—				—				5			4,618				4,618
Commercial Non Real Estate
Rate modification	—			—				—				—			—				—
Term extension	4			217				217				8			125				125
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				1			10				10
Other	—			—				—				—			—				—
Total commercial non real estate	4			217				217				9			135				135
Agriculture
Rate modification	—			—				—				—			—				—
Term extension	—			—				—				2			260				260
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				—			—				—
Total agriculture	—			—				—				2			260				260
Consumer
Rate modification	—			—				—				—			—				—
Term extension	1			1				1				1			11				11
Payment modification	—			—				—				—			—				—
Bankruptcy	—			—				—				—			—				—
Other	—			—				—				1			1				1
Total consumer	1			1				1				2			12				12
Total non-accruing	9			442				442				26			$	5,183			$	5,183
Change in recorded investment due to principal paydown at time of modification	—			—				—				—			—				—
Change in recorded investment due to chargeoffs at time of modification	—			—				—				—			—				—
The tables below represent defaults on loans that were first modified during the respective past 12 months, that became 90 days or more delinquent or were charged-off during the three and six months ended March 31, 2015 and 2014, respectively.
	Three Months Ended
	March 31,
	2015							2014
($ in thousands)	Number of			Recorded				Number of			Recorded
	Loans			Investment				Loans			Investment
Residential real estate	4			$	107			3			$	375
Commercial real estate	—			—				3			1,814
Commercial non real estate	—			—				5			1,604
Agriculture	—			—				6			3,685
Consumer	—			—				—			—
	4			$	107			17			$	7,478
	Six Months Ended
	March 31,
	2015							2014
($ in thousands)	Number of			Recorded				Number of			Recorded
	Loans			Investment				Loans			Investment
Residential real estate	10			$	629			3			$	375
Commercial real estate	—			—				5			8,110
Commercial non real estate	1			95				5			1,604
Agriculture	1			15				7			7,361
Consumer	—			—				—			—
	12			$	739			20			$	17,450

Allowance_for_Loan_Losses_Tabl

Allowance for Loan Losses (Tables)	6 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Allowance for credit losses on financing receivables	The following tables presents the Company’s allowance for loan losses roll forward for the three and six month periods ended March 31, 2015 and 2014.
	Three Months Ended March 31, 2015	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Beginning balance January 1,	$	7,567		$	17,722		$	14,625		$	10,920		$	201		$	785		$	51,820
	2015
	Charge-offs	(63		)	(1,570		)	(8,440		)	(27		)	(19		)	(403		)	(10,522		)
	Recoveries	70			26			983			22			23			325			1,449
	Provision	160			(389		)	8,789			1,307			(17		)	120			9,970
	(Impairment) improvement of	(239		)	(53		)	—			—			1			—			(291		)
	loans acquired with
	deteriorated credit quality
	Ending balance March 31, 2015	$	7,495		$	15,736		$	15,957		$	12,222		$	189		$	827		$	52,426
	Three Months Ended March 31, 2014	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Beginning balance January 1, 2014	$	11,854		$	22,292		$	11,552		$	9,256		$	390		$	725		$	56,069
	Charge-offs	(207		)	(3,194		)	(838		)	(2,086		)	(96		)	(486		)	(6,907		)
	Recoveries	21			433			(128		)	(2		)	31			326			681
	Provision	(216		)	(2,536		)	1,380			735			37			100			(500		)
	(Impairment) improvement of	(1,175		)	608			(1,691		)	—			68			—			(2,190		)
	loans acquired with
	deteriorated credit quality
	Ending balance March 31, 2014	$	10,277		$	17,603		$	10,275		$	7,903		$	430		$	665		$	47,153
	Six Months Ended March 31, 2015	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Beginning balance October 1,	$	8,342		$	16,884		$	10,550		$	10,655		$	264		$	823		$	47,518
	2014
	Charge-offs	(120		)	(1,652		)	(8,524		)	(27		)	(57		)	(831		)	(11,211		)
	Recoveries	113			95			2,143			79			47			644			3,121
	Provision	(190		)	346			11,788			1,515			(41		)	191			13,609
	(Impairment) improvement of	(650		)	63			—			—			(24		)	—			(611		)
	loans acquired with
	deteriorated credit quality
	Ending balance March 31, 2015	$	7,495		$	15,736		$	15,957		$	12,222		$	189		$	827		$	52,426
	Six Months Ended March 31, 2014	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Beginning balance October 1,	$	11,779		$	22,562		$	11,222		$	9,296		$	312		$	693		$	55,864
	2013
	Charge-offs	(437		)	(3,194		)	(999		)	(2,086		)	(152		)	(956		)	(7,824		)
	Recoveries	96			1,024			759			15			67			717			2,678
	Provision	14			(3,397		)	734			678			135			211			(1,625		)
	(Impairment) improvement of	(1,175		)	608			(1,441		)	—			68			—			(1,940		)
	loans acquired with
	deteriorated credit quality
	Ending balance March 31, 2014	$	10,277		$	17,603		$	10,275		$	7,903		$	430		$	665		$	47,153
	The following tables provide details regarding the allowance for loan and lease losses and balance by type of allowance. These tables (in thousands) are presented net of unamortized discount on acquired loans and excludes loans measured at fair value with changes in fair value reported in earnings of $1,060.6 million, loans held for sale of $9.0 million, and guaranteed loans of $112.3 million for March 31, 2015 and loans measured at fair value with changes in fair value reported in earnings of $985.4 million, loans held for sale of $10.4 million, and guaranteed loans of $106.5 million for September 30, 2014.
	As of March 31, 2015	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
		Real Estate			Real Estate			Non Real
								Estate
	Allowance for loan losses
	Individually evaluated for impairment	$	2,721		$	1,691		$	6,894		$	3,007		$	52		$	—		$	14,365
	Collectively evaluated for impairment	2,640			11,274			9,063			9,215			137			827			33,156
	Loans acquired with deteriorated credit quality	2,134			709			—			—			—			—			2,843
	Loans acquired without deteriorated credit quality	—			2,062			—			—			—			—			2,062
	Total allowance	$	7,495		$	15,736		$	15,957		$	12,222		$	189		$	827		$	52,426
	Financing Receivables
	Individually evaluated for impairment	$	9,669		$	62,020		$	39,900		$	36,407		$	177		$	—		$	148,173
	Collectively evaluated for impairment	677,091			2,138,649			1,134,073			1,350,998			76,625			35,433			5,412,869
	Loans acquired with deteriorated credit quality	93,277			27,834			5,348			1,595			1,466			—			129,520
	Loans acquired without deteriorated credit quality	105,259			74,794			8,026			16,102			1,662			—			205,843
	Loans Outstanding	$	885,296		$	2,303,297		$	1,187,347		$	1,405,102		$	79,930		$	35,433		$	5,896,405
As of September 30, 2014	Residential			Commercial			Commercial			Agriculture			Consumer			Other			Total
	Real Estate			Real Estate			Non Real
							Estate
Allowance for loan losses
Individually evaluated for impairment	$	2,528		$	1,953		$	3,909		$	1,152		$	51		$	—		$	9,593
Collectively evaluated for impairment	3,030			12,034			6,641			9,503			188			823			32,219
Loans acquired with deteriorated credit quality	2,784			645			—			—			25			—			3,454
Loans acquired without deteriorated credit quality	—			2,252			—			—			—			—			2,252
Total allowance	$	8,342		$	16,884		$	10,550		$	10,655		$	264		$	823		$	47,518
Financing Receivables
Individually evaluated for impairment	$	9,384		$	38,457		$	28,298		$	25,655		$	166		$	—		$	101,960
Collectively evaluated for impairment	649,970			1,874,474			1,224,035			1,319,343			85,065			34,243			5,187,130
Loans acquired with deteriorated credit quality	102,987			49,202			6,361			1,746			1,843			—			162,139
Loans acquired without deteriorated credit quality	117,630			95,323			7,409			17,655			2,825			—			240,842
Loans Outstanding	$	879,971		$	2,057,456		$	1,266,103		$	1,364,399		$	89,899		$	34,243		$	5,692,071

Accounting_for_Certain_Loans_A1

Accounting for Certain Loans Acquired with Deteriorated Credit Quality (Tables)	6 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Troubled Debt Restructurings on Financing Receivables	The re-assessment of purchased impaired loans resulted in the following changes in the accretable yield during the three and six months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Balance at beginning of period	$	46,342		$	58,411		$	50,889		$	67,660
	Accretion	(3,222		)	(4,944		)	(8,009		)	(9,374		)
	Reclassification from nonaccretable difference	311			2,948			631			2,948
	Disposals	—			—			(80		)	(4,819		)
	Balance at end of period	43,431			56,415			43,431			56,415
Impaired Financing Receivables	The following table presents the Company’s impaired loans (in thousands). This table excludes loans covered by FDIC loss sharing agreements:
		Recorded			Unpaid			Related			Average
		Investment			Principal			Allowance			Recorded
					Balance						Investment
	As of March 31, 2015
	Impaired loans:
	With an allowance recorded:
	Residential real estate	$	12,332		$	12,452		$	2,721		$	12,220
	Commercial real estate	73,729			75,381			1,753			67,942
	Commercial non real estate	41,310			49,834			6,905			36,916
	Agriculture	46,031			46,059			3,007			40,780
	Consumer	268			325			52			274
		$	173,670		$	184,051		$	14,438		$	158,132
		Recorded			Unpaid			Related			Average
		Investment			Principal			Allowance			Recorded
					Balance						Investment
	As of September 30, 2014
	Impaired loans:
	With an allowance recorded:
	Residential real estate	$	12,107		$	12,737		$	2,529		$	13,572
	Commercial real estate	62,155			64,597			2,017			84,490
	Commercial non real estate	32,522			37,882			3,927			31,827
	Agriculture	35,528			37,958			1,155			30,546
	Consumer	280			491			51			346
		$	142,592		$	153,665		$	9,679		$	160,781
	The following table provides purchased impaired loans at March 31, 2015 and September 30, 2014 (in thousands):
		March 31, 2015									30-Sep-14
		Outstanding			Recorded			Carrying			Outstanding			Recorded		Carrying
		Balance 1			Investment 2			Value 3			Balance 1			Investment 2		Value 3
	Residential real estate	$	110,499		$	93,277		$	91,143		$	115,863		$	102,987	$	100,203
	Commercial real estate	107,514			27,835			27,126			130,825			49,202		48,557
	Commercial non real estate	14,710			5,348			5,348			16,697			6,361		6,361
	Agriculture	1,623			1,595			1,595			1,747			1,746		1,746
	Consumer	1,838			1,466			1,466			2,019			1,843		1,818
	Total lending	$	236,184		$	129,521		$	126,678		$	267,151		$	162,139	$	158,685
	1    Represents the legal balance of loans acquired with deteriorated credit quality.
	2    Represents the book balance of loans acquired with deteriorated credit quality.
	3    Represents the book balance of loans acquired with deteriorated credit quality net of the related allowance for loan losses.

FDIC_Indemnification_Asset_Tab

FDIC Indemnification Asset (Tables)	6 Months Ended
	Mar. 31, 2015
Banking and Thrift [Abstract]
FDIC indemnification asset roll forward	The following table represents a summary of the activity related to the FDIC indemnification asset for the three and six months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Balance at beginning of period	$	22,162		$	41,756		$	26,678		$	45,690
	Amortization	(2,060		)	(4,662		)	(4,593		)	(7,947		)
	Changes in expected reimbursements from FDIC for changes in expected credit losses	2			(382		)	(190		)	(408		)
	Changes in reimbursable expenses	(207		)	1,437			(363		)	2,805
	Payments to/(from) the FDIC	(2		)	(374		)	(1,637		)	(2,365		)
	Balance at end of period	$	19,895		$	37,775		$	19,895		$	37,775

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	6 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Positions, Notional Amounts	The following table summarizes the notional amounts and estimated fair values of the Company’s derivative instruments at March 31, 2015 and September 30, 2014 (in thousands).
		March 31, 2015
		Notional				Balance Sheet		Positive Fair				Negative Fair
		Amount				Location		Value				Value
	Derivatives not designated as hedging instruments:
	Interest rate swaps	$	1,045,934			Liabilities		$	71			$	(48,858	)
	Mortgage loan commitments	37,394				Assets		27				—
	Mortgage loan forward sale contracts	44,485				Liabilities		—				(27		)
		September 30, 2014
		Notional				Balance Sheet		Positive Fair				Negative Fair
		Amount				Location		Value				Value
	Derivatives not designated as hedging instruments:
	Interest rate swaps	$	986,440			Liabilities		$	6,213			$	(19,286	)
	Mortgage loan commitments	22,563				Assets		19				—
	Mortgage loan forward sale contracts	28,459				Liabilities		—				(19		)
Schedule of Derivative Instruments, Effect on Other Comprehensive Income	The effect of derivatives on the consolidated statements of comprehensive income for the three and six months ended March 31, 2015 and 2014 (in thousands) was as follows:
				Amount of Gain (Loss) Recognized in Income
				Three Months Ended								Six Months Ended
		Location of		March 31, 2015				March 31, 2014				March 31, 2015				March 31, 2014
		Gain (Loss) Recognized in
		Income
	Derivatives not designated as hedging instruments:
	Interest rate swaps	Noninterest income		$	(21,698	)		$	(12,436	)		$	(46,303	)		$	(7,599	)
	Mortgage loan commitments	Noninterest income		13				31				27				34
	Mortgage loan forward sale contracts	Noninterest income		(13		)		(31		)		(27		)		(34		)
Summary of Offsetting Assets	The following tables (in thousands) present the Company's gross derivative financial assets and liabilities at March 31, 2015 and September 30, 2014, and the related impact of enforceable master netting arrangements and cash collateral, where applicable:
		Gross				Amount				Net Amount				Held/Pledged				Net
		Amount				Offset				Presented in				Financial				Amount
										Consolidated				Instruments1
										Balance Sheets
	March 31, 2015
	Derivative financial assets:
	Derivatives subject to master netting arrangement or similar arrangement	$	71			$	(71	)		$	—			$	—			$	—
	Derivative financial liabilities:
	Derivatives subject to master netting arrangement or similar arrangement	(48,858		)		71				(48,787		)		48,787				—
	Total derivative financial liabilities	$	(48,787	)		$	—			$	(48,787	)		$	48,787			$	—
	1 The actual amount of collateral exceeds the fair value exposure, at the individual counterparty level, as of the date presented.
		Gross				Amount				Net Amount				Held/Pledged				Net
		Amount				Offset				Presented in				Financial				Amount
										Consolidated				Instruments
										Balance Sheets
	September 30, 2014
	Derivative financial assets:
	Derivatives subject to master netting arrangement or similar arrangement	$	6,213			$	(6,213	)		$	—			$	—			$	—
	Derivative financial liabilities:
	Derivatives subject to master netting arrangement or similar arrangement	(19,286		)		6,213				(13,073		)		13,073				—
	Total derivative financial liabilities	$	(13,073	)		$	—			$	(13,073	)		$	13,073			$	—
Summary of Offsetting Liabilities	The following tables (in thousands) present the Company's gross derivative financial assets and liabilities at March 31, 2015 and September 30, 2014, and the related impact of enforceable master netting arrangements and cash collateral, where applicable:
		Gross				Amount				Net Amount				Held/Pledged				Net
		Amount				Offset				Presented in				Financial				Amount
										Consolidated				Instruments1
										Balance Sheets
	March 31, 2015
	Derivative financial assets:
	Derivatives subject to master netting arrangement or similar arrangement	$	71			$	(71	)		$	—			$	—			$	—
	Derivative financial liabilities:
	Derivatives subject to master netting arrangement or similar arrangement	(48,858		)		71				(48,787		)		48,787				—
	Total derivative financial liabilities	$	(48,787	)		$	—			$	(48,787	)		$	48,787			$	—
	1 The actual amount of collateral exceeds the fair value exposure, at the individual counterparty level, as of the date presented.
		Gross				Amount				Net Amount				Held/Pledged				Net
		Amount				Offset				Presented in				Financial				Amount
										Consolidated				Instruments
										Balance Sheets
	September 30, 2014
	Derivative financial assets:
	Derivatives subject to master netting arrangement or similar arrangement	$	6,213			$	(6,213	)		$	—			$	—			$	—
	Derivative financial liabilities:
	Derivatives subject to master netting arrangement or similar arrangement	(19,286		)		6,213				(13,073		)		13,073				—
	Total derivative financial liabilities	$	(13,073	)		$	—			$	(13,073	)		$	13,073			$	—

The_Fair_Value_Option_Tables

The Fair Value Option (Tables)

6 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Summary of Fair Value Option

Changes in fair value for items for which the fair value option has been elected and the line items in which these changes are reported are as follows for the three and six months ended March 31, 2015 and 2014 (in thousands):

For the Three Months Ended

For the Six Months Ended

March 31, 2015

March 31, 2014

March 31, 2015

March 31, 2014

Noninterest

Total Changes

Noninterest

Total Changes

Noninterest

Total Changes

Noninterest

Total Changes

Income

in Fair Value

Income

in Fair Value

Income

in Fair Value

Income

in Fair Value

Long-term loans and written loan commitments

$

15,208

$

15,208

$

8,730

$

8,730

$

32,308

$

32,308

$

(380

)

$

(380

)

Core_Deposits_and_Other_Intang1

Core Deposits and Other Intangibles (Tables)	6 Months Ended
	Mar. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-lived Intangible Assets	A summary of intangible assets subject to amortization is as follows (in thousands):
		Core Deposit			Brand			Customer			Total
		Intangible			Intangible			Relationships
								Intangible
	As of March 31, 2015
	Gross carrying amount	$	92,679		$	8,464		$	16,089		$	117,232
	Accumulated amortization	(90,819		)	(3,854		)	(12,956		)	(107,629		)
	Net intangible assets	$	1,860		$	4,610		$	3,133		$	9,603
	As of September 30, 2014
	Gross carrying amount	$	92,679		$	8,464		$	16,089		$	117,232
	Accumulated amortization	(87,423		)	(3,572		)	(12,008		)	(103,003		)
	Net intangible assets	$	5,256		$	4,892		$	4,081		$	14,229
Schedule of Finite-lived Intangible Assets, Future Amortization Expense	Estimated amortization expense of intangible assets in subsequent fiscal years is as follows (in thousands):
	Remaining in 2015	$	2,484
	2016	2,822
	2017	1,097
	2018	564
	2019	564
	2020 and thereafter	2,072
		$	9,603

FHLB_Advances_Related_Party_No1

FHLB Advances, Related Party Notes Payable and Other Borrowings (Tables)	6 Months Ended
	Mar. 31, 2015
Federal Home Loan Banks [Abstract]
Schedule of FHLB Advances and Other Borrowings	FHLB advances, related party notes payable, and other borrowings consist of the following at March 31, 2015 and September 30, 2014 (in thousands):
		March 31, 2015		September 30, 2014
	Subordinated capital note to NAB New York (a branch of NAB), due June 2018 (callable June 2015), interest paid quarterly based on LIBOR plus 205 basis points, unsecured	$	35,795	$	35,795
	$10,000 revolving line of credit to NAB due on demand, interest paid monthly based on LIBOR plus 125 basis points, unsecured	5,500		5,500
	Total related party notes payable	41,295		41,295
	Notes payable to Federal Home Loan Bank (FHLB), interest rates from 0.21% to 3.66% and maturity dates from April 2015 to July 2023, collateralized by real estate loans and FHLB stock, with various call dates at the option of the FHLB	475,000		575,000
	Other	19		94
	Total FHLB advances and other borrowings	475,019		575,094
		$	516,314	$	616,389
Schedule of FHLB Advances and Other Borrowings by Maturity Date	As of March 31, 2015, FHLB advances, related party notes payable and other borrowings are due or callable (whichever is earlier) in subsequent fiscal years as follows (in thousands):
	Remaining in 2015	$	70,519
	2016	90,000
	2017	25,000
	2018	60,795
	2019	75,000
	2020 and thereafter	195,000
		$	516,314

Income_Taxes_Tables

Income Taxes (Tables)	6 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Schedule of Income Tax Expense (Benefit) Components	The provision for income taxes charged to operations consists of the following for the three and six months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Currently paid or payable
	Federal	$	10,337		$	10,994		$	24,011		$	26,960
	State	1,484			1,288			3,477			3,957
		11,821			12,282			27,488			30,917
	Deferred tax (benefit) expense	(2,101		)	2,207			(4,066		)	(1,489		)
	Income tax expense	$	9,720		$	14,489		$	23,422		$	29,428
Schedule of Effective Income Tax Rate Reconciliation	The income tax provision differs from the amount of income tax determined by applying the U.S. federal income tax rate to pretax income due to the following for the three and six months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Computed “expected” tax expense (35%)	$	10,305		$	14,161		$	24,445		$	29,401
	Increase (decrease) in income taxes resulting from:
	Tax exempt interest income	(1,651		)	(1,174		)	(3,216		)	(2,276		)
	State income taxes, net of federal benefit	965			837			2,260			2,572
	Other	101			665			(67		)	(269		)
	Actual tax expense	$	9,720		$	14,489		$	23,422		$	29,428
Schedule of Deferred Tax Assets and Liabilities	Net deferred tax assets (liabilities) consist of the following components at March 31, 2015 and September 30, 2014 (in thousands):
		March 31, 2015			September 30, 2014
	Deferred tax assets:
	Allowance for loan losses	$	21,421		$	19,683
	Compensation	606			329
	Net operating loss carryforward	94			119
	Securities available for sale	(1,310		)	3,758
	Other real estate owned	15,462			13,721
	Core deposit intangible and other fair value adjustments	11,227			10,573
	Excess tax basis of loans acquired over carrying value	8,438			9,595
	Other	4,976			6,272
	Total deferred tax assets	60,914			64,050
	Deferred tax liabilities:
	Goodwill and other intangibles	(3,707		)	(9,099		)
	Premises and equipment	(11,037		)	(4,390		)
	Excess carrying value of FDIC indemnification asset and clawback liability	(1,557		)	(4,280		)
	Other	(912		)	(1,578		)
	Total deferred tax liabilities	(17,213		)	(19,347		)
	Net deferred tax assets	$	43,701		$	44,703

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	6 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-Based Compensation, Restricted Stock Units Award Activity	The following is a summary of the Plans’ restricted share and performance-based stock award activity as of March 31, 2015:
	Restricted Shares	Common Shares		Weighted-Average
				Grant Date
				Fair Value
	Restricted shares, October 1, 2014	—		$	—
	Granted	79,728		18.05
	Vested and issued	—		—
	Forfeited	(556	)	18
	Canceled	—		—
	Restricted shares, March 31, 2015	79,172		$	18.05
	Vested, but not issuable at March 31, 2015	12,221		$	18
	Performance Shares
	Performance shares, October 1, 2014	—		$	—
	Granted	221,184		18
	Vested and issued	—		—
	Forfeited	(4,736	)	18
	Canceled	—		—
	Performance shares, March 31, 2015	216,448		$	18

Fair_Value_of_Financial_Instru1

Fair Value of Financial Instruments and Interest Rate Risk (Tables)	6 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Schedule of Fair Value Measurements, Assets and Liabilities	The following table presents the fair value measurements of assets and liabilities recognized in the accompanying consolidated balance sheets measured at fair value on a recurring basis and the level within the fair value hierarchy in which the fair value measurements fall at March 31, 2015 and September 30, 2014 (in thousands):
		Fair Value				Level 1				Level 2				Level 3
	As of March 31, 2015
	U.S. Treasury securities	$	275,477			$	275,477			$	—			$	—
	U.S. Agency securities	74,801				—				74,801				—
	Mortgage-backed securities	1,044,021				—				1,044,021				—
	States and political subdivision securities	2,108				—				150				1,958
	Corporate debt securities	5,062				—				5,062				—
	Other	1,039				—				1,039				—
	Securities available for sale	$	1,402,508			$	275,477			$	1,125,073			$	1,958
	Derivatives-assets	$	27			$	—			$	27			$	—
	Derivatives-liabilities	48,814				—				48,814				—
	Fair value loans and written loan	1,060,598				—				1,060,598				—
	commitments
		Fair Value				Level 1				Level 2				Level 3
	As of September 30, 2014
	U.S. Treasury securities	$	222,725			$	222,725			$	—			$	—
	U.S. Agency securities	—				—				—				—
	Mortgage-backed securities	1,103,415				—				1,103,415				—
	States and political subdivision securities	2,189				—				160				2,029
	Corporate debt securities	11,873				—				11,873				—
	Other	1,040				—				1,040				—
	Securities available for sale	$	1,341,242			$	222,725			$	1,116,488			$	2,029
	Derivatives-assets	$	19			$	—			$	19			$	—
	Derivatives-liabilities	13,092				—				13,092				—
	Fair value loans and written loan	985,411				—				985,411				—
	commitments
Schedule of Available-for-Sale Securities Reconciliation	The following table presents the changes in Level 3 financial instruments for the three months ended March 31, 2015 and 2014 (in thousands):
		Other Securities Available for Sale
	Balance as of December 31, 2014	$	1,958
	Principal paydown	—
	Balance as of March 31, 2015	$	1,958
	Balance as of December 31, 2013	$	2,243
	Principal paydown	—
	Balance as of March 31, 2014	$	2,243
	The following table presents the changes in Level 3 financial instruments for the six months ended March 31, 2015 and 2014 (in thousands):
		Other Securities Available for Sale
	Balance as of September 30, 2014	$	2,029
	Principal paydown	(71		)
	Balance as of March 31, 2015	$	1,958
	Balance as of September 30, 2013	$	2,243
	Principal paydown	—
	Balance as of March 31, 2014	$	2,243
Mortgage Loans Held-for-Sale, Fair Value Measurement	The following tables present the fair value measurement of assets and liabilities measured at fair value on a nonrecurring basis and the level within the fair value hierarchy in which the fair value measurements fall at March 31, 2015 and September 30, 2014 (in thousands):
		Fair Value				Level 1				Level 2				Level 3
	As of March 31, 2015
	Other real estate owned	$	25,162			$	—			$	—			$	25,162
	Impaired loans	161,904				—				—				161,904
	Loans held for sale, at lower of cost or fair	9,006				—				9,006				—
	value
	As of September 30, 2014
	Other real estate owned	$	36,879			$	—			$	—			$	36,879
	Impaired loans	111,265				—				—				111,265
	Loans held for sale, at lower of cost or fair	10,381				—				10,381				—
	value
Mortgage Loans Held-for-Sale, Recurring and Nonrecurring Fair Value Measurements	The valuation techniques and significant unobservable inputs used to measure Level 3 fair value measurements at March 31, 2015 were as follows (in thousands):
	Financial	Fair Value of Assets / (Liabilities) at March 31, 2015				Valuation		Unobservable		Range		Weighted
	Instrument					Technique(s)		Input				Average
	Other real estate	$	25,162			Appraisal value		Property specific adjustment		N/A		N/A
	owned
	Impaired loans	$	161,904			Appraisal value		Property		N/A		N/A
								specific adjustment
Fair Value, by Balance Sheet Grouping	Fair values for balance sheet instruments as of March 31, 2015 and September 30, 2014, are as follows (in thousands):
				March 31, 2015								September 30, 2014
		Level in		Carrying				Fair Value				Carrying				Fair Value
		Fair Value		Amount								Amount
		Hierarchy
	Assets
	Cash and due from banks	Level 1		$	358,440			$	358,440			$	256,639			$	256,639
	Loans, net excluding fair valued loans and loans	Level 3		5,950,437				5,935,242				5,744,157				5,734,274
	held for sale
	Accrued interest receivable	Level 2		37,933				37,933				42,609				42,609
	Federal Home Loan Bank stock	Level 2		31,810				31,810				35,922				35,922
	Liabilities
	Deposits	Level 3		$	7,487,698			$	7,499,432			$	7,052,180			$	7,057,591
	FHLB advances, related party notes payable, and other borrowings	Level 2		516,314				510,339				616,389				604,615
	Securities sold under repurchase agreements	Level 2		163,343				163,343				161,687				161,687
	Accrued interest payable	Level 2		4,469				4,469				5,273				5,273
	Subordinated debentures	Level 2		56,083				56,084				56,083				56,084

Earnings_per_Share_Tables

Earnings per Share (Tables)	6 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Earnings per Share	The following information was used in the computation of basic earnings per share (EPS) for the three and six months ended March 31, 2015 and 2014 (in thousands except share data).
		Three Months Ended				Six Months Ended
		March 31,				March 31,
		2015		2014		2015		2014
	Net income	$	19,724	$	25,971	$	46,421	$	54,575
	Weighted average common shares outstanding	57,898,335		57,886,114		57,897,059		57,886,114
	Dilutive effect of stock based compensation	18,467		—		9,234		—
	Weighted average common shares outstanding for diluted earnings per share calculation	57,916,802		57,886,114		57,906,293		57,886,114
	Basic earnings per share	$	0.34	$	0.45	$	0.8	$	0.94
	Diluted earnings per share	$	0.34	$	0.45	$	0.8	$	0.94

Basis_of_Presentation_Schedule

Basis of Presentation - Schedule of Error Correction on Realized Gain (Loss) on Derivatives (Details) (USD $)	6 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Noninterest income
Realized gain (loss) on derivatives	($8,678)	($6,668)	($18,255)	($14,217)	($9,931)
Immaterial error correction | Interest income
Realized gain (loss) on derivatives	($8,678)	($6,668)	($18,255)	($14,217)	($9,931)

Basis_of_Presentation_Schedule1

Basis of Presentation - Schedule of Fair Value of Loans, Correction (Details) (USD $)	3 Months Ended		6 Months Ended			12 Months Ended			0 Months Ended
In Thousands, except Share data in Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Apr. 28, 2015	6-May-15
Dividends declared per share (in dollars per share)	$0.12	$0.59	$0.12	$0.59
Change in fair value of loans	$15,208	$8,730	$32,308	($380)
Net increase (decrease) in fair value of loans at fair value | Adjustment
Loan fair value change related to interest rates				1,078	14,124	-11,922	40,305	-19,369
Loan fair value change related to credit quality				-698	-396	18	855	4,276
Reclassification adjustment				380	13,728	-11,904	41,160	-15,093
Derivatives, net realized and unrealized gain (loss) | Adjustment
Reclassification adjustment				-1,078	-14,124	11,922	-40,305	19,369
Subsequent event
Dividends declared per share (in dollars per share)									$0.12
Change in presentation of changes in fair value of fair value loans | Interest income | Previously Reported
Loan fair value change related to interest rates				1,078	14,124	-11,922	40,305	-19,369
Loan fair value change related to credit quality				-698	-396	18	855	4,276
Change in fair value of loans				380	13,728	-11,904	41,160	-15,093
Change in presentation of gain (loss) for derivatives related to fair value loans | Noninterest expense | Previously Reported
Unrealized gain (loss) on derivatives				($1,078)	($14,124)	$11,922	($40,305)	$19,369
National Australia Bank Limited | Subsequent event
Number of shares sold by company										23
Shares sold by parent, percentage of company stock										39.70%
Ownership percentage by parent										28.50%

Restrictions_on_Cash_and_Due_f1

Restrictions on Cash and Due from Banks (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Millions, unless otherwise specified
Cash and Cash Equivalents [Abstract]
Reserve balances	$40.20	$50.40

Securities_Available_for_Sale_1

Securities Available for Sale - (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]
Proceeds from sale of available-for-sale securities	$0	$4,500,000	$55,100,000	$4,500,000
Available-for-sale securities, gross realized gains	0	0	600,000	0
Available-for-sale securities, gross realized losses	0	0	500,000	0
Securities pledged as collateral	1,174,900,000		1,174,900,000		1,132,300,000
Percentage of investment portfolio in continuous loss position	40.00%		40.00%		64.00%
Federal home loan bank stock	$31,800,000		$31,800,000		$35,900,000

Securities_Available_for_Sale_2

Securities Available for Sale - Amortized Cost and Fair Value (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized	$1,399,087	$1,351,157
Gross Unrealized Gains	8,546	4,846
Gross Unrealized Losses	-5,125	-14,761
Fair Value	1,402,508	1,341,242
U.S. Treasury securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized	271,753	222,868
Gross Unrealized Gains	3,724	31
Gross Unrealized Losses	0	-174
Fair Value	275,477	222,725
U.S. Agency securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized	74,345	0
Gross Unrealized Gains	456	0
Gross Unrealized Losses	0	0
Fair Value	74,801	0
States and political subdivision securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized	2,107	2,188
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Fair Value	2,108	2,189
Corporate debt securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized	4,996	11,732
Gross Unrealized Gains	66	141
Gross Unrealized Losses	0	0
Fair Value	5,062	11,873
Other
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized	1,006	1,006
Gross Unrealized Gains	33	34
Gross Unrealized Losses	0	0
Fair Value	1,039	1,040
Government National Mortgage Association | Mortgage backed-securities, Issued by US Government
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized	945,299	1,113,363
Gross Unrealized Gains	4,266	4,639
Gross Unrealized Losses	-4,469	-14,587
Fair Value	945,096	1,103,415
Federal National Mortgage Association | Mortgage backed-securities, Issued by US Government
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized	48,495	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	-129	0
Fair Value	48,366	0
Small Business Assistance Program | Mortgage backed-securities, Issued by US Government
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized	51,086	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	-527	0
Fair Value	$50,559	$0

Securities_Available_for_Sale_3

Securities Available for Sale - Schedule of Available For Sale Securities (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Amortized Cost
Due in one year or less	$76,162	$7,207
Due after one year through five years	272,043	223,282
Due after five years through ten years	4,996	6,299
Amortized Cost	353,201	236,788
Fair Value
Due in one year or less	76,620	7,218
Due after one year through five years	275,766	223,140
Due after five years through ten years	5,062	6,429
Fair Value	357,448	236,787
Amortized Cost	1,399,087	1,351,157
Fair Value	1,402,508	1,341,242
Securities without contractual maturities, Amortized Cost	1,006	1,006
Securities without contractual maturities, Fair Value	1,039	1,040
Mortgage-backed securities
Fair Value
Amortized Cost	1,044,880	1,113,363
Fair Value	$1,044,021	$1,103,415

Securities_Available_for_Sale_4

Securities Available for Sale - Schedule of Gross Unrealized Losses (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Fair Value	$83,704	$122,969
12 months or more, Fair Value	479,290	730,171
Fair Value	562,994	853,140
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized	-656	-299
12 months or more, Unrealized	-4,469	-14,462
Unrealized	-5,125	-14,761
U.S. Treasury securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Fair Value	0	98,344
12 months or more, Fair Value	0	0
Fair Value	0	98,344
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized	0	-174
12 months or more, Unrealized	0	0
Unrealized	0	-174
U.S. Agency securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Fair Value	0	0
12 months or more, Fair Value	0	0
Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized	0	0
12 months or more, Unrealized	0	0
Unrealized	0	0
Mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Fair Value	83,704	24,625
12 months or more, Fair Value	479,290	730,171
Fair Value	562,994	754,796
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized	-656	-125
12 months or more, Unrealized	-4,469	-14,462
Unrealized	-5,125	-14,587
Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Fair Value	0	0
12 months or more, Fair Value	0	0
Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized	0	0
12 months or more, Unrealized	0	0
Unrealized	0	0
Other
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Fair Value	0	0
12 months or more, Fair Value	0	0
Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized	0	0
12 months or more, Unrealized	0	0
Unrealized	$0	$0

Securities_Available_for_Sale_5

Securities Available for Sale - Unrealized Gain (Loss) On Investments (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Beginning balance accumulated other comprehensive income (loss)	($3,042)	($13,535)	($6,157)	($7,081)
Net unrealized holding gain (loss) arising during the period	8,312	10,020	13,285	-389
Reclassification adjustment for net gain realized in net income	0	-6	-51	-6
Net change in unrealized gain (loss) before income taxes	8,312	10,014	13,234	-395
Income tax (expense) benefit	-3,159	-3,693	-4,966	262
Net change in unrealized gain (loss) on securities after taxes	5,153	6,321	8,268	-133
Ending balance accumulated other comprehensive income (loss)	$2,111	($7,214)	$2,111	($7,214)

Loans_Narrative_Details

Loans - Narrative (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans covered by FDIC loss share agreements	$187,649,000		$187,649,000		$234,036,000
Loan held for sale	9,006,000		9,006,000		10,381,000
Loans and written loan commitments at fair value under the fair value option	1,060,598,000		1,060,598,000		985,411,000
Unamortized discount on acquired loans	6,500,000		6,500,000		6,300,000
Loans in process	-700,000		-700,000		600,000
Loans guaranteed by U.S. Government Agencies	5,896,405,000		5,896,405,000		5,692,071,000
Principal balances of residential real estate loans sold	69,600,000	33,700,000	133,900,000	87,800,000
Interest income recognized on impaired loans	1,800,000	2,100,000	4,800,000	3,300,000
Valuation adjustments made to repossessed properties	2,200,000	500,000	4,300,000	1,000,000
Specific reserves included in the allowance for loan losses for TDRs	2,700,000		2,700,000		3,200,000
Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and written loan commitments at fair value under the fair value option	1,060,600,000		1,060,600,000			985,400,000
Loans Guaranteed by US Government Authorities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans guaranteed by U.S. Government Agencies	$112,300,000		$112,300,000		$106,500,000

Loans_Schedule_of_Financing_Re

Loans - Schedule of Financing Receivable (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	$7,100,060		$6,819,977
Allowance for loan losses	-52,426	-51,820	-47,518	-47,153	-56,069	-55,864
Unamortized discount on acquired loans	-21,774		-25,638
Unearned net deferred fees and costs and loans in process	-5,821		-6,872
Total financing receivables, net	7,020,039		6,739,949
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	905,114		901,605
Allowance for loan losses	-7,495	-7,567	-8,342	-10,277	-11,854	-11,779
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	2,673,255		2,541,194
Allowance for loan losses	-15,736	-17,722	-16,884	-17,603	-22,292	-22,562
Commercial non real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	1,657,856		1,571,640
Allowance for loan losses	-15,957	-14,625	-10,550	-10,275	-11,552	-11,222
Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	1,748,366		1,681,209
Allowance for loan losses	-12,222	-10,920	-10,655	-7,903	-9,256	-9,296
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	80,036		90,086
Allowance for loan losses	-189	-201	-264	-430	-390	-312
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	35,433		34,243
Allowance for loan losses	($827)	($785)	($823)	($665)	($725)	($693)

Loans_Past_Due_Loans_Details

Loans - Past Due Loans (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	$46,512	$43,945
Financing receivables, net of unamortized discount on acquired loans	5,830,035	5,574,881
Loans covered by FDIC loss sharing agreements	187,649	234,036
Total	6,017,684	5,808,917
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	7,690	6,671
Financing receivables, net of unamortized discount on acquired loans	782,544	764,754
Loans covered by FDIC loss sharing agreements	113,578	127,115
Total	896,122	891,869
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	10,836	20,767
Financing receivables, net of unamortized discount on acquired loans	2,292,179	2,003,838
Loans covered by FDIC loss sharing agreements	63,268	95,467
Total	2,355,447	2,099,305
Commercial non real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	9,015	4,908
Financing receivables, net of unamortized discount on acquired loans	1,229,587	1,312,658
Loans covered by FDIC loss sharing agreements	8,925	9,390
Total	1,238,512	1,322,048
Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	18,860	11,453
Financing receivables, net of unamortized discount on acquired loans	1,410,408	1,369,549
Loans covered by FDIC loss sharing agreements	1,832	2,004
Total	1,412,240	1,371,553
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	111	146
Financing receivables, net of unamortized discount on acquired loans	79,884	89,839
Loans covered by FDIC loss sharing agreements	46	60
Total	79,930	89,899
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	35,433	34,243
Loans covered by FDIC loss sharing agreements	0	0
Total	35,433	34,243
Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	5,804,579	5,542,128
Loans covered by FDIC loss sharing agreements	179,923	227,096
Total	5,984,502	5,769,224
Current | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	777,219	760,887
Current | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	2,284,882	1,988,585
Current | Commercial non real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	1,221,359	1,303,925
Current | Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	1,406,083	1,364,960
Current | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	79,603	89,528
Current | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	35,433	34,243
Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	25,456	32,753
Loans covered by FDIC loss sharing agreements	7,726	6,940
Total	33,182	39,693
Past Due | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	5,325	3,867
Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	7,297	15,253
Past Due | Commercial non real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	8,228	8,733
Past Due | Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	4,325	4,589
Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	281	311
Past Due | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	0	0
Past Due | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	9,127	13,746
Loans covered by FDIC loss sharing agreements	4,744	1,960
Total	13,871	15,706
Past Due | 30-59 Days Past Due | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	1,909	675
Past Due | 30-59 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	165	11,050
Past Due | 30-59 Days Past Due | Commercial non real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	3,344	1,761
Past Due | 30-59 Days Past Due | Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	3,491	16
Past Due | 30-59 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	218	244
Past Due | 30-59 Days Past Due | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	0	0
Past Due | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	3,528	8,044
Loans covered by FDIC loss sharing agreements	214	1,252
Total	3,742	9,296
Past Due | 60-89 Days Past Due | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	562	611
Past Due | 60-89 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	2,316	819
Past Due | 60-89 Days Past Due | Commercial non real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	622	6,228
Past Due | 60-89 Days Past Due | Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	0	368
Past Due | 60-89 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	28	18
Past Due | 60-89 Days Past Due | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	0	0
Past Due | Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	12,801	10,963
Loans covered by FDIC loss sharing agreements	2,768	3,728
Total	15,569	14,691
Past Due | Greater Than 90 Days | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	2,854	2,581
Past Due | Greater Than 90 Days | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	4,816	3,384
Past Due | Greater Than 90 Days | Commercial non real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	4,262	744
Past Due | Greater Than 90 Days | Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	834	4,205
Past Due | Greater Than 90 Days | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	35	49
Past Due | Greater Than 90 Days | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	$0	$0

Loans_Composition_of_the_Loan_

Loans - Composition of the Loan Portfolio by Internal Risk Rating (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	$5,830,035	$5,574,881
Loans covered by FDIC loss share agreements	187,649	234,036
Total	6,017,684	5,808,917
Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	5,284,331	5,159,494
Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	384,448	287,723
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	156,475	125,830
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	4,722	1,659
Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	59	175
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	782,544	764,754
Loans covered by FDIC loss share agreements	113,578	127,115
Total	896,122	891,869
Residential real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	765,058	747,485
Residential real estate | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	5,248	5,320
Residential real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	11,759	11,290
Residential real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	428	659
Residential real estate | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	51	0
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	2,292,179	2,003,838
Loans covered by FDIC loss share agreements	63,268	95,467
Total	2,355,447	2,099,305
Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	2,122,618	1,867,866
Commercial real estate | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	105,838	84,132
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	63,540	51,692
Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	183	148
Commercial real estate | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Commercial non real estate
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	1,229,587	1,312,658
Loans covered by FDIC loss share agreements	8,925	9,390
Total	1,238,512	1,322,048
Commercial non real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	1,093,867	1,218,558
Commercial non real estate | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	96,724	65,628
Commercial non real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	36,627	27,499
Commercial non real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	2,369	798
Commercial non real estate | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	175
Agriculture
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	1,410,408	1,369,549
Loans covered by FDIC loss share agreements	1,832	2,004
Total	1,412,240	1,371,553
Agriculture | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	1,188,111	1,202,145
Agriculture | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	176,266	132,262
Agriculture | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	44,290	35,107
Agriculture | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	1,741	35
Agriculture | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	79,884	89,839
Loans covered by FDIC loss share agreements	46	60
Total	79,930	89,899
Consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	79,244	89,197
Consumer | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	372	381
Consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	259	242
Consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	1	19
Consumer | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	8	0
Other
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	35,433	34,243
Loans covered by FDIC loss share agreements	0	0
Total	35,433	34,243
Other | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	35,433	34,243
Other | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Other | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Other | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Other | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	$0	$0

Loans_Impaired_Financing_Recei

Loans - Impaired Financing Receivables (Details) (USD $)	6 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014
Financing Receivable, Impaired [Line Items]
Recorded Investment	$173,670	$142,592
Unpaid Principal Balance	184,051	153,665
Related Allowance	14,438	9,679
Average Recorded Investment	158,132	160,781
Residential real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment	12,332	12,107
Unpaid Principal Balance	12,452	12,737
Related Allowance	2,721	2,529
Average Recorded Investment	12,220	13,572
Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment	73,729	62,155
Unpaid Principal Balance	75,381	64,597
Related Allowance	1,753	2,017
Average Recorded Investment	67,942	84,490
Commercial non real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment	41,310	32,522
Unpaid Principal Balance	49,834	37,882
Related Allowance	6,905	3,927
Average Recorded Investment	36,916	31,827
Agriculture
Financing Receivable, Impaired [Line Items]
Recorded Investment	46,031	35,528
Unpaid Principal Balance	46,059	37,958
Related Allowance	3,007	1,155
Average Recorded Investment	40,780	30,546
Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment	268	280
Unpaid Principal Balance	325	491
Related Allowance	52	51
Average Recorded Investment	$274	$346

Loans_Troubled_Debt_Restructur

Loans - Troubled Debt Restructurings on Accruing and Nonaccrual Financing Receivables (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014
	contract	contract	contract	contract
Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$58,122		$58,122		$36,857
Financing receivable, modifications, number of contracts	13	7	17	18
Financing receivable, modifications, pre-modification recorded investment	7,219	451	27,957	4,117
Financing receivable, modifications, post-modification recorded investment	7,129	451	27,867	4,117
Change in recorded investment due to principal paydown at time of modification, number of contracts	0	0	0	0
Change in recorded investment due to principal paydown at time of modification, pre-modification	0	0	0	0
Change in recorded investment due to principal paydown at time of modification, post-modification		0		0
Change in recorded investment due to chargeoffs at time of modification, number of contracts	1	0	1	0
Change in recorded investment due to chargeoffs at time of modification, pre-modification	90	0	90	0
Change in recorded investment due to chargeoffs at time of modification, post-modification	0	0	0	0
Accruing | Residential real estate
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	618		618		1,112
Financing receivable, modifications, number of contracts	2	0	2	4
Financing receivable, modifications, pre-modification recorded investment	36	0	36	219
Financing receivable, modifications, post-modification recorded investment	36	0	36	219
Accruing | Commercial real estate
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	45,160		45,160		25,177
Financing receivable, modifications, number of contracts	6	0	8	1
Financing receivable, modifications, pre-modification recorded investment	4,248	0	23,130	1,070
Financing receivable, modifications, post-modification recorded investment	4,158	0	23,040	1,070
Accruing | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	10,165		10,165		6,753
Financing receivable, modifications, number of contracts	4	4	6	9
Financing receivable, modifications, pre-modification recorded investment	2,929	429	4,785	2,796
Financing receivable, modifications, post-modification recorded investment	2,929	429	4,785	2,796
Accruing | Agriculture
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	2,159		2,159		3,780
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Consumer
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	20		20		35
Financing receivable, modifications, number of contracts	1	3	1	4
Financing receivable, modifications, pre-modification recorded investment	6	22	6	32
Financing receivable, modifications, post-modification recorded investment	6	22	6	32
Accruing | Rate modification | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	1	0	1	0
Financing receivable, modifications, pre-modification recorded investment	15	0	15	0
Financing receivable, modifications, post-modification recorded investment	15	0	15	0
Accruing | Rate modification | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Rate modification | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	1	0
Financing receivable, modifications, pre-modification recorded investment	0	0	32	0
Financing receivable, modifications, post-modification recorded investment	0	0	32	0
Accruing | Rate modification | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Rate modification | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Term extension | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	2
Financing receivable, modifications, pre-modification recorded investment	0	0	0	74
Financing receivable, modifications, post-modification recorded investment	0	0	0	74
Accruing | Term extension | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	1	0	1	0
Financing receivable, modifications, pre-modification recorded investment	90	0	90	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Term extension | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	3	1	3	4
Financing receivable, modifications, pre-modification recorded investment	2,879	35	2,879	1,734
Financing receivable, modifications, post-modification recorded investment	2,879	35	2,879	1,734
Accruing | Term extension | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Term extension | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Payment modification | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	1
Financing receivable, modifications, pre-modification recorded investment	0	0	0	15
Financing receivable, modifications, post-modification recorded investment	0	0	0	15
Accruing | Payment modification | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	4	0	6	1
Financing receivable, modifications, pre-modification recorded investment	3,660	0	22,542	1,070
Financing receivable, modifications, post-modification recorded investment	3,660	0	22,542	1,070
Accruing | Payment modification | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	1	2	2	4
Financing receivable, modifications, pre-modification recorded investment	50	67	1,874	735
Financing receivable, modifications, post-modification recorded investment	50	67	1,874	735
Accruing | Payment modification | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Payment modification | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	2	0	2
Financing receivable, modifications, pre-modification recorded investment	0	4	0	4
Financing receivable, modifications, post-modification recorded investment	0	4	0	4
Accruing | Bankruptcy | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	1
Financing receivable, modifications, pre-modification recorded investment	0	0	0	130
Financing receivable, modifications, post-modification recorded investment	0	0	0	130
Accruing | Bankruptcy | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	1	0	1	0
Financing receivable, modifications, pre-modification recorded investment	498	0	498	0
Financing receivable, modifications, post-modification recorded investment	498	0	498	0
Accruing | Bankruptcy | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Bankruptcy | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Bankruptcy | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	1	0	1	0
Financing receivable, modifications, pre-modification recorded investment	6	0	6	0
Financing receivable, modifications, post-modification recorded investment	6	0	6	0
Accruing | Other | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	1	0	1	0
Financing receivable, modifications, pre-modification recorded investment	21	0	21	0
Financing receivable, modifications, post-modification recorded investment	21	0	21	0
Accruing | Other | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Other | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	1	0	1
Financing receivable, modifications, pre-modification recorded investment	0	327	0	327
Financing receivable, modifications, post-modification recorded investment	0	327	0	327
Accruing | Other | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Accruing | Other | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	1	0	2
Financing receivable, modifications, pre-modification recorded investment	0	18	0	28
Financing receivable, modifications, post-modification recorded investment	0	18	0	28
Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	15,188		15,188		20,415
Financing receivable, modifications, number of contracts	9	13	9	26
Financing receivable, modifications, pre-modification recorded investment	442	5,001	442	5,183
Financing receivable, modifications, post-modification recorded investment	442	5,001	442	5,183
Change in recorded investment due to principal paydown at time of modification, number of contracts	0	0	0	0
Change in recorded investment due to principal paydown at time of modification, pre-modification	0	0	0	0
Change in recorded investment due to principal paydown at time of modification, post-modification	0	0	0	0
Change in recorded investment due to chargeoffs at time of modification, number of contracts	0	0	0	0
Change in recorded investment due to chargeoffs at time of modification, pre-modification	0	0	0	0
Change in recorded investment due to chargeoffs at time of modification, post-modification	0	0	0	0
Nonaccrual | Residential real estate
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	1,929		1,929		1,730
Financing receivable, modifications, number of contracts	4	5	4	8
Financing receivable, modifications, pre-modification recorded investment	224	113	224	158
Financing receivable, modifications, post-modification recorded investment	224	113	224	158
Nonaccrual | Commercial real estate
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	5,424		5,424		6,884
Financing receivable, modifications, number of contracts	0	5	0	5
Financing receivable, modifications, pre-modification recorded investment	0	4,618	0	4,618
Financing receivable, modifications, post-modification recorded investment	0	4,618	0	4,618
Nonaccrual | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	1,445		1,445		1,785
Financing receivable, modifications, number of contracts	4	1	4	9
Financing receivable, modifications, pre-modification recorded investment	217	10	217	135
Financing receivable, modifications, post-modification recorded investment	217	10	217	135
Nonaccrual | Agriculture
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	6,377		6,377		9,994
Financing receivable, modifications, number of contracts	0	2	0	2
Financing receivable, modifications, pre-modification recorded investment	0	260	0	260
Financing receivable, modifications, post-modification recorded investment	0	260	0	260
Nonaccrual | Consumer
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	13		13		22
Financing receivable, modifications, number of contracts	1	0	1	2
Financing receivable, modifications, pre-modification recorded investment	1	0	1	12
Financing receivable, modifications, post-modification recorded investment	1	0	1	12
Nonaccrual | Rate modification | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	2	4	2	4
Financing receivable, modifications, pre-modification recorded investment	104	98	104	98
Financing receivable, modifications, post-modification recorded investment	104	98	104	98
Nonaccrual | Rate modification | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	2	0	2
Financing receivable, modifications, pre-modification recorded investment	0	500	0	500
Financing receivable, modifications, post-modification recorded investment	0	500	0	500
Nonaccrual | Rate modification | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Rate modification | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Rate modification | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Term extension | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	1	1	1	2
Financing receivable, modifications, pre-modification recorded investment	77	15	77	18
Financing receivable, modifications, post-modification recorded investment	77	15	77	18
Nonaccrual | Term extension | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	2	0	2
Financing receivable, modifications, pre-modification recorded investment	0	4,031	0	4,031
Financing receivable, modifications, post-modification recorded investment	0	4,031	0	4,031
Nonaccrual | Term extension | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	4	0	4	8
Financing receivable, modifications, pre-modification recorded investment	217	0	217	125
Financing receivable, modifications, post-modification recorded investment	217	0	217	125
Nonaccrual | Term extension | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	2	0	2
Financing receivable, modifications, pre-modification recorded investment	0	260	0	260
Financing receivable, modifications, post-modification recorded investment	0	260	0	260
Nonaccrual | Term extension | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	1	0	1	1
Financing receivable, modifications, pre-modification recorded investment	1	0	1	11
Financing receivable, modifications, post-modification recorded investment	1	0	1	11
Nonaccrual | Payment modification | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Payment modification | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Payment modification | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Payment modification | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Payment modification | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Bankruptcy | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	1	0	1	1
Financing receivable, modifications, pre-modification recorded investment	43	0	43	4
Financing receivable, modifications, post-modification recorded investment	43	0	43	4
Nonaccrual | Bankruptcy | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Bankruptcy | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	1	0	1
Financing receivable, modifications, pre-modification recorded investment	0	10	0	10
Financing receivable, modifications, post-modification recorded investment	0	10	0	10
Nonaccrual | Bankruptcy | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Bankruptcy | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Other | Residential real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	1
Financing receivable, modifications, pre-modification recorded investment	0	0	0	38
Financing receivable, modifications, post-modification recorded investment	0	0	0	38
Nonaccrual | Other | Commercial real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	1	0	1
Financing receivable, modifications, pre-modification recorded investment	0	87	0	87
Financing receivable, modifications, post-modification recorded investment	0	87	0	87
Nonaccrual | Other | Commercial non real estate
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Other | Agriculture
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	0
Financing receivable, modifications, pre-modification recorded investment	0	0	0	0
Financing receivable, modifications, post-modification recorded investment	0	0	0	0
Nonaccrual | Other | Consumer
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	0	0	0	1
Financing receivable, modifications, pre-modification recorded investment	0	0	0	1
Financing receivable, modifications, post-modification recorded investment	$0	$0	$0	$1

Loans_Subsequent_Defaults_on_M

Loans - Subsequent Defaults on Modified Loans (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
	contract	contract	contract	contract
Financing Receivable, Modifications [Line Items]
Number of Loans	4	17	12	20
Recorded Investment	$107	$7,478	$739	$17,450
Residential real estate
Financing Receivable, Modifications [Line Items]
Number of Loans	4	3	10	3
Recorded Investment	107	375	629	375
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Loans	0	3	0	5
Recorded Investment	0	1,814	0	8,110
Commercial non real estate
Financing Receivable, Modifications [Line Items]
Number of Loans	0	5	1	5
Recorded Investment	0	1,604	95	1,604
Agriculture
Financing Receivable, Modifications [Line Items]
Number of Loans	0	6	1	7
Recorded Investment	0	3,685	15	7,361
Consumer
Financing Receivable, Modifications [Line Items]
Number of Loans	0	0	0	0
Recorded Investment	$0	$0	$0	$0

Allowance_for_Loan_Losses_Narr

Allowance for Loan Losses - (Narrative) (Details) (USD $)	6 Months Ended	12 Months Ended
	Mar. 31, 2015	Sep. 30, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and written loan commitments at fair value under the fair value option	$1,060,598,000	$985,411,000
Loan held for sale	9,006,000	10,381,000
Guaranteed loans	112,300,000	106,500,000
Unfunded loan commitment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$400,000	$400,000

Allowance_for_Loan_Losses_Summ

Allowance for Loan Losses - Summary of Allowance for Loan Losses (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	$51,820	$56,069	$47,518	$55,864
Charge-offs	-10,522	-6,907	-11,211	-7,824
Recoveries	1,449	681	3,121	2,678
Provision	9,970	-500	13,609	-1,625
Allowance for loan losses, ending balance	52,426	47,153	52,426	47,153
Residential real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	7,567	11,854	8,342	11,779
Charge-offs	-63	-207	-120	-437
Recoveries	70	21	113	96
Provision	160	-216	-190	14
Allowance for loan losses, ending balance	7,495	10,277	7,495	10,277
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	17,722	22,292	16,884	22,562
Charge-offs	-1,570	-3,194	-1,652	-3,194
Recoveries	26	433	95	1,024
Provision	-389	-2,536	346	-3,397
Allowance for loan losses, ending balance	15,736	17,603	15,736	17,603
Commercial non real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	14,625	11,552	10,550	11,222
Charge-offs	-8,440	-838	-8,524	-999
Recoveries	983	-128	2,143	759
Provision	8,789	1,380	11,788	734
Allowance for loan losses, ending balance	15,957	10,275	15,957	10,275
Agriculture
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	10,920	9,256	10,655	9,296
Charge-offs	-27	-2,086	-27	-2,086
Recoveries	22	-2	79	15
Provision	1,307	735	1,515	678
Allowance for loan losses, ending balance	12,222	7,903	12,222	7,903
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	201	390	264	312
Charge-offs	-19	-96	-57	-152
Recoveries	23	31	47	67
Provision	-17	37	-41	135
Allowance for loan losses, ending balance	189	430	189	430
Other
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	785	725	823	693
Charge-offs	-403	-486	-831	-956
Recoveries	325	326	644	717
Provision	120	100	191	211
Allowance for loan losses, ending balance	827	665	827	665
Receivables acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			3,454
(Impairment) improvement of loans acquired with deteriorated credit quality	-291	-2,190	-611	-1,940
Allowance for loan losses, ending balance	2,843		2,843
Receivables acquired with deteriorated credit quality | Residential real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			2,784
(Impairment) improvement of loans acquired with deteriorated credit quality	-239	-1,175	-650	-1,175
Allowance for loan losses, ending balance	2,134		2,134
Receivables acquired with deteriorated credit quality | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			645
(Impairment) improvement of loans acquired with deteriorated credit quality	-53	608	63	608
Allowance for loan losses, ending balance	709		709
Receivables acquired with deteriorated credit quality | Commercial non real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			0
(Impairment) improvement of loans acquired with deteriorated credit quality	0	-1,691	0	-1,441
Allowance for loan losses, ending balance	0		0
Receivables acquired with deteriorated credit quality | Agriculture
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			0
(Impairment) improvement of loans acquired with deteriorated credit quality	0	0	0	0
Allowance for loan losses, ending balance	0		0
Receivables acquired with deteriorated credit quality | Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			25
(Impairment) improvement of loans acquired with deteriorated credit quality	1	68	-24	68
Allowance for loan losses, ending balance	0		0
Receivables acquired with deteriorated credit quality | Other
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			0
(Impairment) improvement of loans acquired with deteriorated credit quality	0	0	0	0
Allowance for loan losses, ending balance	$0		$0

Allowance_for_Loan_Losses_Summ1

Allowance for Loan Losses - Summary of Allowance for Loan Losses by Type (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$14,365		$9,593
Collectively evaluated for impairment	33,156		32,219
Total allowance	52,426	51,820	47,518	47,153	56,069	55,864
Financing Receivable, Net [Abstract]
Individually evaluated for impairment	148,173		101,960
Collectively evaluated for impairment	5,412,869		5,187,130
Financing receivable	5,896,405		5,692,071
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	2,721		2,528
Collectively evaluated for impairment	2,640		3,030
Total allowance	7,495	7,567	8,342	10,277	11,854	11,779
Financing Receivable, Net [Abstract]
Individually evaluated for impairment	9,669		9,384
Collectively evaluated for impairment	677,091		649,970
Financing receivable	885,296		879,971
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,691		1,953
Collectively evaluated for impairment	11,274		12,034
Total allowance	15,736	17,722	16,884	17,603	22,292	22,562
Financing Receivable, Net [Abstract]
Individually evaluated for impairment	62,020		38,457
Collectively evaluated for impairment	2,138,649		1,874,474
Financing receivable	2,303,297		2,057,456
Commercial non real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	6,894		3,909
Collectively evaluated for impairment	9,063		6,641
Total allowance	15,957	14,625	10,550	10,275	11,552	11,222
Financing Receivable, Net [Abstract]
Individually evaluated for impairment	39,900		28,298
Collectively evaluated for impairment	1,134,073		1,224,035
Financing receivable	1,187,347		1,266,103
Agriculture
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,007		1,152
Collectively evaluated for impairment	9,215		9,503
Total allowance	12,222	10,920	10,655	7,903	9,256	9,296
Financing Receivable, Net [Abstract]
Individually evaluated for impairment	36,407		25,655
Collectively evaluated for impairment	1,350,998		1,319,343
Financing receivable	1,405,102		1,364,399
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	52		51
Collectively evaluated for impairment	137		188
Total allowance	189	201	264	430	390	312
Financing Receivable, Net [Abstract]
Individually evaluated for impairment	177		166
Collectively evaluated for impairment	76,625		85,065
Financing receivable	79,930		89,899
Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	827		823
Total allowance	827	785	823	665	725	693
Financing Receivable, Net [Abstract]
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	35,433		34,243
Financing receivable	35,433		34,243
Receivables acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	2,843		3,454
Financing Receivable, Net [Abstract]
Financing receivable	129,520		162,139
Receivables acquired with deteriorated credit quality | Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	2,134		2,784
Financing Receivable, Net [Abstract]
Financing receivable	93,277		102,987
Receivables acquired with deteriorated credit quality | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	709		645
Financing Receivable, Net [Abstract]
Financing receivable	27,834		49,202
Receivables acquired with deteriorated credit quality | Commercial non real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0		0
Financing Receivable, Net [Abstract]
Financing receivable	5,348		6,361
Receivables acquired with deteriorated credit quality | Agriculture
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0		0
Financing Receivable, Net [Abstract]
Financing receivable	1,595		1,746
Receivables acquired with deteriorated credit quality | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0		25
Financing Receivable, Net [Abstract]
Financing receivable	1,466		1,843
Receivables acquired with deteriorated credit quality | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0		0
Financing Receivable, Net [Abstract]
Financing receivable	0		0
Receivables acquired without deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	2,062		2,252
Financing Receivable, Net [Abstract]
Financing receivable	205,843		240,842
Receivables acquired without deteriorated credit quality | Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0		0
Financing Receivable, Net [Abstract]
Financing receivable	105,259		117,630
Receivables acquired without deteriorated credit quality | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	2,062		2,252
Financing Receivable, Net [Abstract]
Financing receivable	74,794		95,323
Receivables acquired without deteriorated credit quality | Commercial non real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0		0
Financing Receivable, Net [Abstract]
Financing receivable	8,026		7,409
Receivables acquired without deteriorated credit quality | Agriculture
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0		0
Financing Receivable, Net [Abstract]
Financing receivable	16,102		17,655
Receivables acquired without deteriorated credit quality | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0		0
Financing Receivable, Net [Abstract]
Financing receivable	1,662		2,825
Receivables acquired without deteriorated credit quality | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0		0
Financing Receivable, Net [Abstract]
Financing receivable	$0		$0

Accounting_for_Certain_Loans_A2

Accounting for Certain Loans Acquired with Deteriorated Credit Quality - Narrative (Details) (USD $)	3 Months Ended		6 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Receivables [Abstract]
Allowance recognized on previous impairments	$0.40	$3.60	$0.90	$3.60

Accounting_for_Certain_Loans_A3

Accounting for Certain Loans Acquired with Deteriorated Credit Quality - Schedule of Troubled Debt Restructurings (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	$46,342	$58,411	$50,889	$67,660
Accretion	-3,222	-4,944	-8,009	-9,374
Reclassification from nonaccretable difference	311	2,948	631	2,948
Disposals	0	0	-80	-4,819
Balance at end of period	$43,431	$56,415	$43,431	$56,415

Accounting_for_Certain_Loans_A4

Accounting for Certain Loans Acquired with Deteriorated Credit Quality - Schedule of Impaired Loans (Details) (USD $)	Mar. 31, 2015		Sep. 30, 2014
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	$236,184	[1]	$267,151	[1]
Recorded Investment	129,521	[2]	162,139	[2]
Carrying Value	126,678	[3]	158,685	[3]
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	110,499	[1]	115,863	[1]
Recorded Investment	93,277	[2]	102,987	[2]
Carrying Value	91,143	[3]	100,203	[3]
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	107,514	[1]	130,825	[1]
Recorded Investment	27,835	[2]	49,202	[2]
Carrying Value	27,126	[3]	48,557	[3]
Commercial non real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	14,710	[1]	16,697	[1]
Recorded Investment	5,348	[2]	6,361	[2]
Carrying Value	5,348	[3]	6,361	[3]
Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	1,623	[1]	1,747	[1]
Recorded Investment	1,595	[2]	1,746	[2]
Carrying Value	1,595	[3]	1,746	[3]
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	1,838	[1]	2,019	[1]
Recorded Investment	1,466	[2]	1,843	[2]
Carrying Value	$1,466	[3]	$1,818	[3]
[1]	Represents the legal balance of loans acquired with deteriorated credit quality
[2]	Represents the book balance of loans acquired with deteriorated credit quality
[3]	Represents the book balance of loans acquired with deteriorated credit quality net of the related allowance for loan losses.

FDIC_Indemnification_Asset_Sch

FDIC Indemnification Asset - Schedule of Other Current Assets (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
FDIC Indemnification Asset [Roll Forward]
Balance at beginning of year	$22,162	$41,756	$26,678	$45,690
Amortization	-2,060	-4,662	-4,593	-7,947
Changes in expected reimbursements from FDIC for changes in expected credit losses	2	-382	-190	-408
Changes in reimbursable expenses	-207	1,437	-363	2,805
Payments to/(from) the FDIC	-2	-374	-1,637	-2,365
Balance at end of year	$19,895	$37,775	$19,895	$37,775

Derivative_Financial_Instrumen2

Derivative Financial Instruments - (Narrative) (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative, collateral, right to reclaim cash	$0	$0

Derivative_Financial_Instrumen3

Derivative Financial Instruments - Notional Amounts and Estimated Fair Value (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Derivative [Line Items]
Negative Fair Value	($48,787)	($13,073)
Assets | Not Designated as Hedging Instruments | Mortgage loan commitments
Derivative [Line Items]
Notional Amount	37,394	22,563
Positive Fair Value	27	19
Negative Fair Value	0	0
Liabilities | Not Designated as Hedging Instruments | Interest rate swaps
Derivative [Line Items]
Notional Amount	1,045,934	986,440
Positive Fair Value	71	6,213
Negative Fair Value	-48,858	-19,286
Liabilities | Not Designated as Hedging Instruments | Mortgage loan forward sale contracts
Derivative [Line Items]
Notional Amount	44,485	28,459
Positive Fair Value	0	0
Negative Fair Value	($27)	($19)

Derivative_Financial_Instrumen4

Derivative Financial Instruments - Effect on the Consolidated Statement of Comprehensive Income (Details) (Noninterest income, USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Interest rate swaps
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Income	($21,698)	($12,436)	($46,303)	($7,599)
Mortgage loan commitments
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Income	13	31	27	34
Mortgage loan forward sale contracts
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Income	($13)	($31)	($27)	($34)

Derivative_Financial_Instrumen5

Derivative Financial Instruments - Offsetting Liabilities and Assets (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Offsetting Assets [Line Items]
Derivative financial liabilities, gross amount	($48,787)	($13,073)
Derivative financial liabilities, amount offset	0	0
Derivative financial liabilities, net amount presented in consolidated balance sheets	-48,787	-13,073
Held/pledged financial instruments	48,787	13,073
Derivative financial liabilities, net amount	0	0
Derivatives subject to master netting arrangement or similar arrangement
Offsetting Assets [Line Items]
Derivative financial liabilities, gross amount	-48,858	-19,286
Derivative financial liabilities, amount offset	71	6,213
Derivative financial liabilities, net amount presented in consolidated balance sheets	-48,787	-13,073
Held/pledged financial instruments	48,787	13,073
Derivative financial liabilities, net amount	0	0
Derivatives subject to master netting arrangement or similar arrangement
Offsetting Assets [Line Items]
Derivative financial assets, gross amount	71	6,213
Derivative financial assets, amount offset	-71	-6,213
Derivative financial assets, net amount presented in consolidated balance sheets	0	0
Held/pledged financial instruments	0	0
Derivative financial assets, net amount	$0	$0

The_Fair_Value_Option_Narrativ

The Fair Value Option - (Narrative) (Details) (USD $)	6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Eligible item for the fair value option	$43.30	$7.10
Long-term loans and written loan commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Eligible item for the fair value option	0.5		-1.2	0.7	0.7
Fair value, option, aggregate differences, long-term debt instruments	$1,017.30	$978.30	$1,017.30

The_Fair_Value_Option_Schedule

The Fair Value Option - Schedule of Fair Value Option (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net increase (decrease) in fair value of loans at fair value	$15,208	$8,730	$32,308	($380)
Long-term loans and written loan commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net increase (decrease) in fair value of loans at fair value	15,208	8,730	32,308	-380
Noninterest income | Long-term loans and written loan commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net increase (decrease) in fair value of loans at fair value	$15,208	$8,730	$32,308	($380)

Core_Deposits_and_Other_Intang2

Core Deposits and Other Intangibles (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense of intangible assets	$2.30	$4.70	$4.60	$9.40

Core_Deposits_and_Other_Intang3

Core Deposits and Other Intangibles - Intangible Assets Amortization Expense (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$117,232	$117,232
Accumulated amortization	-107,629	-103,003
Core deposits and other intangibles	9,603	14,229
Core Deposit Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	92,679	92,679
Accumulated amortization	-90,819	-87,423
Core deposits and other intangibles	1,860	5,256
Brand Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	8,464	8,464
Accumulated amortization	-3,854	-3,572
Core deposits and other intangibles	4,610	4,892
Customer Relationships Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	16,089	16,089
Accumulated amortization	-12,956	-12,008
Core deposits and other intangibles	$3,133	$4,081

Core_Deposits_and_Other_Intang4

Core Deposits and Other Intangibles - Schedule of Future Amortization Expense (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
Remaining in 2015	$2,484
2016	2,822
2017	1,097
2018	564
2019	564
2020 and thereafter	2,072
Core deposits and other intangibles	$9,603	$14,229

Securities_Sold_Under_Agreemen1

Securities Sold Under Agreements to Repurchase - (Narrative) (Details) (USD $)	6 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014
Offsetting Assets [Line Items]
Securities sold under agreements to repurchase	176.7	$190.60
Securities sold under agreements to repurchase, fair value of collateral	177.2	$188.60
Minimum
Offsetting Assets [Line Items]
Securities sold under agreements to repurchase, maturity period	1 day
Maximum
Offsetting Assets [Line Items]
Securities sold under agreements to repurchase, maturity period	4 days

FHLB_Advances_Related_Party_No2

FHLB Advances, Related Party Notes Payable and Other Borrowings - (Narrative) (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Millions, unless otherwise specified
Federal Home Loan Banks [Abstract]
Current borrowing capacity	$796.30
Loans pledged to the Federal Home Loan Bank	$2,157.10	$2,145.50

FHLB_Advances_Related_Party_No3

FHLB Advances, Related Party Notes Payable and Other Borrowings - Schedule of Advances, Related Party Notes (Details) (USD $)	6 Months Ended	12 Months Ended
	Mar. 31, 2015	Sep. 30, 2014
Debt Instrument [Line Items]
Related party notes payable	41,295,000	41,295,000
Notes payable	475,000,000	575,000,000
Other	19,000	94,000
Total FHLB advances and other borrowings	475,019,000	575,094,000
Financing receivable	516,314,000	616,389,000
Subordinated Capital Note to NAB New York due June 2018
Debt Instrument [Line Items]
Related party notes payable	35,795,000	35,795,000
Revolving line of credit to NAB
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	10,000,000	10,000,000
Related party notes payable	5,500,000	5,500,000
Subordinated debt | Subordinated Capital Note to NAB New York due June 2018 | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	2.05%	2.05%
Subordinated debt | Notes Payable to FHLB collateralized by real estate loans, due 2023 | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Stated interest rate, percentage	0.21%	0.21%
Subordinated debt | Notes Payable to FHLB collateralized by real estate loans, due 2023 | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Stated interest rate, percentage	3.66%	3.66%
Line of credit | Revolving line of credit to NAB | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	1.25%	1.25%

FHLB_Advances_Related_Party_No4

FHLB Advances, Related Party Notes Payable and Other Borrowings - Schedule of Due or Callable Notes (Details) (FHLB Advances and Related Party Notes Payable, USD $)	Mar. 31, 2015
In Thousands, unless otherwise specified
FHLB Advances and Related Party Notes Payable
Debt Instrument [Line Items]
Remaining in 2015	$70,519
2016	90,000
2017	25,000
2018	60,795
2019	75,000
2020 and thereafter	195,000
Total	$516,314

Income_Taxes_Narrative_Details

Income Taxes - (Narrative) (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
Income Tax Contingency [Line Items]
Income tax payable	$0	$4,915,000
Internal Revenue Service (IRS)
Income Tax Contingency [Line Items]
Income taxes receivable	200,000
National Americas Investment, Inc
Income Tax Contingency [Line Items]
Income tax payable		$4,900,000

Income_Taxes_Reconciliation_of

Income Taxes - Reconciliation of Income Tax Expense (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Income Tax Disclosure [Abstract]
Federal	$10,337	$10,994	$24,011	$26,960
State	1,484	1,288	3,477	3,957
Current income tax expense (benefit)	11,821	12,282	27,488	30,917
Deferred tax benefit	-2,101	2,207	-4,066	-1,489
Income tax expense	$9,720	$14,489	$23,422	$29,428

Income_Taxes_Schedule_of_Effec

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Income Tax Disclosure [Abstract]
Income tax percentage	35.00%	35.00%	35.00%	35.00%
Tax at statutory rate (35%)	$10,305	$14,161	$24,445	$29,401
Tax exempt interest income	-1,651	-1,174	-3,216	-2,276
State income taxes, net of federal benefit	965	837	2,260	2,572
Other	101	665	-67	-269
Income tax expense	$9,720	$14,489	$23,422	$29,428

Income_Taxes_Schedule_of_Defer

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Deferred tax assets:
Allowance for loan losses	$21,421	$19,683
Compensation	606	329
Net operating loss carryforward	94	119
Securities available for sale	-1,310	3,758
Other real estate owned	15,462	13,721
Core deposit intangible and other fair value adjustments	11,227	10,573
Excess tax basis of loans acquired over carrying value	8,438	9,595
Other	4,976	6,272
Total deferred tax assets	60,914	64,050
Deferred tax liabilities:
Goodwill and other intangibles	-3,707	-9,099
Premises and equipment	-11,037	-4,390
Excess carrying value of FDIC indemnification asset and clawback liability	-1,557	-4,280
Other	-912	-1,578
Total deferred tax liabilities	-17,213	-19,347
Net deferred tax assets	$43,701	$44,703

ProfitSharing_Plan_Details

Profit-Sharing Plan - (Details) (Multiple employer 401(k) profit sharing plan, USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Multiple employer 401(k) profit sharing plan
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, requisite service period			1 year
Defined contribution plan, minimum age requirement			21 years
Contributions by the Company	$500,000	$0	$1,800,000	$1,200,000

StockBased_Compensation_Narrat

Stock-Based Compensation - (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award, award vesting period			3 years
Share-based compensation expense	$200,000	$0	$700,000	$0
Tax benefit from compensation expense	100,000	0	300,000	0
Target performance level			100.00%
Share-based compensation, compensation cost not yet recognized	$2,500,000		$2,500,000
Share-based compensation, compensation cost not yet recognized, recognition period			2 years 6 months
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-established target levels			0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target performance level			150.00%
Pre-established target levels			150.00%
Performance shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares to be issued (approximately)			324,672

StockBased_Compensation_Schedu

Stock-Based Compensation - Schedule of Restricted and Performance Stock (Details) (USD $)	6 Months Ended
	Mar. 31, 2015	Sep. 30, 2014
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Shares, beginning of year (shares)	0
Granted (shares)	79,728
Vested and issued (shares)	0
Forfeited (shares)	-556
Canceled (shares)	0
Shares, beginning of year (shares)	79,172
Vested, but not issuable (shares)	12,221
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Shares, beginning of year (in USD per share)	$18.05	$0
Granted (in USD per share)	$18.05
Vested and issued (in USD per share)	$0
Forfeited (in USD per share)	$18
Canceled (in USD per share)	$0
Shares, beginning of year (in USD per share)	$18.05	$0
Vested, but not issuable (in USD per share)	$18
Performance shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Shares, beginning of year (shares)	0
Granted (shares)	221,184
Vested and issued (shares)	0
Forfeited (shares)	-4,736
Canceled (shares)	0
Shares, beginning of year (shares)	216,448
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Shares, beginning of year (in USD per share)	$18	$0
Granted (in USD per share)	$18
Vested and issued (in USD per share)	$0
Forfeited (in USD per share)	$18
Canceled (in USD per share)	$0
Shares, beginning of year (in USD per share)	$18	$0

Fair_Value_of_Financial_Instru2

Fair Value of Financial Instruments and Interest Rate Risk - (Narrative) (Details)	6 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Derivative, remaining maturity	180 days

Fair_Value_of_Financial_Instru3

Fair Value of Financial Instruments and Interest Rate Risk - Schedule of Fair Value Measurements of Assets and Liabilities (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	$1,402,508	$1,341,242
Derivatives-liabilities	48,814	13,092
Fair value loans and written loan commitments	1,060,598	985,411
Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,402,508	1,341,242
Derivative-assets	27	19
Derivatives-liabilities	48,814	13,092
Fair value loans and written loan commitments	1,060,598	985,411
Fair value, measurements, recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	275,477	222,725
Derivative-assets	0	0
Derivatives-liabilities	0	0
Fair value loans and written loan commitments	0	0
Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,125,073	1,116,488
Derivative-assets	27	19
Derivatives-liabilities	48,814	13,092
Fair value loans and written loan commitments	1,060,598	985,411
Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,958	2,029
Derivative-assets	0	0
Derivatives-liabilities	0	0
Fair value loans and written loan commitments	0	0
U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	275,477	222,725
U.S. Treasury securities | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	275,477	222,725
U.S. Treasury securities | Fair value, measurements, recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	275,477	222,725
U.S. Treasury securities | Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
U.S. Treasury securities | Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
U.S. Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	74,801	0
U.S. Agency securities | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	74,801	0
U.S. Agency securities | Fair value, measurements, recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
U.S. Agency securities | Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	74,801	0
U.S. Agency securities | Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,044,021	1,103,415
Mortgage-backed securities | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,044,021	1,103,415
Mortgage-backed securities | Fair value, measurements, recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
Mortgage-backed securities | Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,044,021	1,103,415
Mortgage-backed securities | Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
States and political subdivision securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,108	2,189
States and political subdivision securities | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,108	2,189
States and political subdivision securities | Fair value, measurements, recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
States and political subdivision securities | Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	150	160
States and political subdivision securities | Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,958	2,029
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	5,062	11,873
Corporate debt securities | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	5,062	11,873
Corporate debt securities | Fair value, measurements, recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
Corporate debt securities | Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	5,062	11,873
Corporate debt securities | Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
Other | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,039	1,040
Other | Fair value, measurements, recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
Other | Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,039	1,040
Other | Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	$0	$0

Fair_Value_of_Financial_Instru4

Fair Value of Financial Instruments and Interest Rate Risk - Schedule of Other Available-for-Sale (Details) (Available-for-sale securities, USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Available-for-sale securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$1,958	$2,243	$2,029	$2,243
Principal paydown	0	0	-71	0
Ending Balance	$1,958	$2,243	$1,958	$2,243

Fair_Value_of_Financial_Instru5

Fair Value of Financial Instruments and Interest Rate Risk - Mortgage Loans Held for Sale (Details) (Fair value, measurements, nonrecurring, USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other real estate owned	$25,162	$36,879
Impaired loans	161,904	111,265
Loans held for sale, at lower of cost or fair value	9,006	10,381
Level 1
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other real estate owned	0	0
Impaired loans	0	0
Loans held for sale, at lower of cost or fair value	0	0
Level 2
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other real estate owned	0	0
Impaired loans	0	0
Loans held for sale, at lower of cost or fair value	9,006	10,381
Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other real estate owned	25,162	36,879
Impaired loans	161,904	111,265
Loans held for sale, at lower of cost or fair value	$0	$0

Fair_Value_of_Financial_Instru6

Fair Value of Financial Instruments and Interest Rate Risk - Level 3 Schedule (Details) (Fair value, measurements, nonrecurring, USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other real estate owned	$25,162	$36,879
Impaired loans	161,904	111,265
Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other real estate owned	25,162	36,879
Impaired loans	$161,904	$111,265

Fair_Value_of_Financial_Instru7

Fair Value of Financial Instruments and Interest Rate Risk - Schedule of Balance Sheet Grouping Fair Value (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Level 1 | Carrying Amount
Assets
Cash and due from banks	$358,440	$256,639
Level 1 | Fair Value
Assets
Cash and due from banks	358,440	256,639
Level 2 | Carrying Amount
Assets
Accrued interest receivable	37,933	42,609
Federal Home Loan Bank stock	31,810	35,922
Liabilities
FHLB advances, related party notes payable, and other borrowings	516,314	616,389
Securities sold under repurchase agreements	163,343	161,687
Accrued interest payable	4,469	5,273
Subordinated debentures	56,083	56,083
Level 2 | Fair Value
Assets
Accrued interest receivable	37,933	42,609
Federal Home Loan Bank stock	31,810	35,922
Liabilities
FHLB advances, related party notes payable, and other borrowings	510,339	604,615
Securities sold under repurchase agreements	163,343	161,687
Accrued interest payable	4,469	5,273
Subordinated debentures	56,084	56,084
Level 3 | Carrying Amount
Assets
Loans, net excluding fair valued loans and loans held for sale	5,950,437	5,744,157
Liabilities
Deposits	7,487,698	7,052,180
Level 3 | Fair Value
Assets
Loans, net excluding fair valued loans and loans held for sale	5,935,242	5,734,274
Liabilities
Deposits	$7,499,432	$7,057,591

Earnings_per_Share_Schedule_of

Earnings per Share - Schedule of EPS, Basic and Diluted (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income	$19,724	$25,971	$46,421	$54,575
Weighted average common shares outstanding	57,898,335	57,886,114	57,897,059	57,886,114
Dilutive effect of stock based compensation (in shares)	18,467	0	9,234	0
Weighted average common shares outstanding for diluted earnings per share calculation	57,916,802	57,886,114	57,906,293	57,886,114
Basic earnings per share (in dollars per share)	$0.34	$0.45	$0.80	$0.94
Diluted earnings per share (in dollars per share)	$0.34	$0.45	$0.80	$0.94
Performance shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share			216,448	0
Stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share			1,665	0