Great Western Bancorp (GWB) 10-Q 8 May 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Mar. 31, 2018	May 01, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	Great Western Bancorp, Inc.
Entity Central Index Key	1,613,665
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		58,896,189

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Assets
Cash and due from banks	$ 168,357	$ 170,657
Interest-bearing bank deposits	203,392	189,739
Cash and cash equivalents	371,749	360,396
Securities available for sale	1,307,598	1,367,960
Loans, net of unearned discounts and deferred fees, including $50,727 and $57,537 of loans covered by a FDIC loss share agreement at March 31, 2018 and September 30, 2017, respectively, and $920,965 and $1,016,576 of loans at fair value under the fair value option at March 31, 2018 and September 30, 2017, respectively, and $2,429 and $7,456 of loans held for sale at March 31, 2018 and September 30, 2017, respectively	9,338,306	8,968,553
Allowance for loan and lease losses	(65,139)	(63,503)
Net loans	9,273,167	8,905,050
Premises and equipment, including $1,109 and $5,147 of property held for sale at March 31, 2018 and September 30, 2017, respectively	107,048	112,209
Accrued interest receivable	49,353	53,176
Other repossessed property, including $86 and $0 of property covered by FDIC loss share agreements at March 31, 2018 and September 30, 2017, respectively	16,726	8,985
Goodwill	739,023	739,023
Cash surrender value of life insurance policies	30,032	29,619
Net deferred tax assets	31,629	42,400
Other assets	65,992	71,193
Total assets	11,992,317	11,690,011
Deposits
Noninterest-bearing	1,854,734	1,856,126
Interest-bearing	7,532,233	7,121,487
Total deposits	9,386,967	8,977,613
Securities sold under agreements to repurchase	103,291	132,636
FHLB advances and other borrowings	551,003	643,214
Subordinated debentures and subordinated notes payable	108,385	108,302
Accrued expenses and other liabilities	53,973	73,246
Total liabilities	10,203,619	9,935,011
Stockholders’ equity
Common stock, $0.01 par value, authorized 500,000,000 shares; 58,896,189 shares issued and outstanding at March 31, 2018 and 58,834,066 shares issued and outstanding at September 30, 2017	589	588
Additional paid-in capital	1,316,150	1,314,039
Retained earnings	494,312	445,747
Accumulated other comprehensive (loss)	(22,353)	(5,374)
Total stockholders' equity	1,788,698	1,755,000
Total liabilities and stockholders' equity	$ 11,992,317	$ 11,690,011

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Assets
Loans covered by FDIC loss share agreements	$ 50,727	$ 57,537
Loans and written loan commitments at fair value under the fair value option	920,965	1,016,576
Loan held for sale	2,429	7,456
Property held for sale	1,109	5,147
Property covered under FDIC loss share agreements	$ 86	$ 0
Stockholders’ equity
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	58,896,189	58,834,066
Common stock, shares outstanding (in shares)	58,896,189	58,834,066

Consolidated Statements of Inco

Consolidated Statements of Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Interest income
Loans	$ 109,993	$ 99,481	$ 217,674	$ 199,413
Investment securities	7,013	6,538	14,055	12,916
Federal funds sold and other	227	219	458	565
Total interest income	117,233	106,238	232,187	212,894
Interest expense
Deposits	12,658	7,829	23,656	15,118
FHLB advances and other borrowings	2,815	1,567	4,978	2,953
Subordinated debentures and subordinated notes payable	1,207	1,098	2,377	2,186
Total interest expense	16,680	10,494	31,011	20,257
Net interest income	100,553	95,744	201,176	192,637
Provision for loan and lease losses	4,900	4,009	9,457	11,058
Net interest income after provision for loan and lease losses	95,653	91,735	191,719	181,579
Noninterest income
Service charges and other fees	12,047	13,574	25,224	27,410
Wealth management fees	2,335	2,429	4,519	4,683
Mortgage banking income, net	1,166	1,640	2,826	4,302
Net (loss) gain on sale of securities	(8)	44	(9)	44
Net (decrease) in fair value of loans at fair value	(14,838)	(5,216)	(23,502)	(69,218)
Net realized and unrealized gain on derivatives	14,282	1,592	21,509	60,568
Other	3,758	1,426	4,849	3,357
Total noninterest income	18,742	15,489	35,416	31,146
Noninterest expense
Salaries and employee benefits	33,672	32,370	66,539	64,004
Data processing and communication	9,190	6,879	16,074	13,595
Occupancy and equipment	5,290	5,123	10,138	9,946
Professional fees	4,027	3,559	8,267	6,394
Advertising	1,121	995	2,181	1,970
Net loss recognized on repossessed property and other related expenses	1,000	397	1,214	1,056
Amortization of core deposits and other intangibles	426	550	852	1,389
Acquisition expenses	0	0	0	710
Other	4,418	3,979	8,747	7,325
Total noninterest expense	59,144	53,852	114,012	106,389
Income before income taxes	55,251	53,372	113,123	106,336
Provision for income taxes	14,719	18,210	43,361	34,271
Net income	$ 40,532	$ 35,162	$ 69,762	$ 72,065
Basic earnings per common share
Weighted average shares outstanding (in shares)	58,941,315	58,788,802	58,921,972	58,769,662
Earnings per share (in dollars per share)	$ 0.69	$ 0.60	$ 1.18	$ 1.23
Diluted earnings per common share
Weighted average shares outstanding (in shares)	59,146,117	59,073,669	59,116,923	59,032,787
Diluted earnings per share (in dollars per share)	$ 0.69	$ 0.60	$ 1.18	$ 1.22
Dividends per share
Dividends paid	$ 11,780	$ 9,989	$ 23,550	$ 19,970
Dividends per share (in dollars per share)	$ 0.20	$ 0.17	$ 0.40	$ 0.34

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 40,532	$ 35,162	$ 69,762	$ 72,065
Securities available for sale:
Net unrealized holding (loss) gain arising during the period	(12,425)	1,815	(21,070)	(19,653)
Reclassification adjustment for net loss (gain) realized in net income	8	(44)	9	(44)
Income tax benefit (expense)	3,062	(673)	6,345	7,485
Net change in unrealized (loss) gain on securities available for sale	(9,355)	1,098	(14,716)	(12,212)
Defined benefit pension plan obligation:
Net unrealized holding gain arising during the year	0	0	145	0
Income tax (expense)	0	0	(55)	0
Net change in defined benefit pension plan obligation	0	0	90	0
Other comprehensive (loss) gain, net of tax	(9,355)	1,098	(14,626)	(12,212)
Comprehensive income	$ 31,177	$ 36,260	$ 55,136	$ 59,853

Consolidated Statement of Stock

Consolidated Statement of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands		Total	Comprehensive Income	Common Stock Par Value	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance at Sep. 30, 2016		$ 1,663,391		$ 587	$ 1,312,347	$ 344,923	$ 5,534
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		72,065	$ 72,065			72,065
Other comprehensive (loss), net of tax		(12,212)	(12,212)				(12,212)
Comprehensive income		59,853	59,853
Stock-based compensation, net of tax		3,587			3,587
Common stock cash dividends		(19,970)				(19,970)
Ending balance at Mar. 31, 2017		1,706,861		587	1,315,934	397,018	(6,678)
Beginning balance at Sep. 30, 2017		1,755,000		588	1,314,039	445,747	(5,374)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		69,762	69,762			69,762
Other comprehensive (loss), net of tax		(14,626)	(14,626)				(14,626)
Comprehensive income		55,136	$ 55,136
Stock-based compensation, net of tax		2,112		1	2,111
Reclassification due to adoption of ASU 2018-02	[1]	0				2,353	(2,353)
Common stock cash dividends		(23,550)				(23,550)
Ending balance at Mar. 31, 2018		$ 1,788,698		$ 589	$ 1,316,150	$ 494,312	$ (22,353)
[1]	Reclassification due to adoption of ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. See Note 2, New Accounting Pronouncements and Note 15, Income Taxes, for additional information.

Consolidated Statement of Stoc7

Consolidated Statement of Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Stockholders' Equity [Abstract]
Cash dividends paid on common stock (in dollars per share)	$ 0.20	$ 0.17

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net income	$ 69,762	$ 72,065
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	5,943	7,984
Amortization of FDIC indemnification asset	1,689	1,981
Net loss on sale of securities and other assets	2,143	1,061
Gain on redemption of subordinated debentures	0	(111)
Net gain on sale of loans	(3,314)	(5,180)
Provision for loan and lease losses	9,457	11,058
Reversal of provision for loan servicing rights loss	(71)	(10)
Stock-based compensation	2,112	3,587
Originations of residential real estate loans held for sale	(112,731)	(137,061)
Proceeds from sales of residential real estate loans held for sale	121,072	150,257
Net deferred income taxes	17,215	(328)
Changes in:
Accrued interest receivable	3,823	5,841
Other assets	423	1,063
Accrued interest payable and other liabilities	(18,336)	(77,655)
Net cash provided by operating activities	99,187	34,552
Investing activities
Purchase of securities available for sale	(110,741)	(183,678)
Proceeds from sales of securities available for sale	25,206	5,042
Proceeds from maturities of securities available for sale	122,436	122,760
Net increase in loans	(392,109)	(36,433)
Payment of covered losses from FDIC indemnification claims	(419)	(218)
Purchase of premises and equipment	(3,297)	(2,830)
Proceeds from sale of premises and equipment	4,565	3,868
Proceeds from sale of repossessed property	2,050	3,453
Purchase of FHLB stock	(30,420)	(4,240)
Proceeds from redemption of FHLB stock	34,251	28,751
Net cash used in investing activities	(348,478)	(63,525)
Financing activities
Net increase in deposits	409,509	487,502
Net decrease in securities sold under agreements to repurchase and other short-term borrowings	(29,345)	(17,216)
Proceeds from FHLB advances and other long-term borrowings	419,999	93,600
Repayments on FHLB advances and other long-term borrowings	(512,200)	(700,000)
Redemption of subordinated debentures	0	(3,625)
Taxes paid related to net share settlement of equity awards	(3,769)	0
Dividends paid	(23,550)	(19,970)
Net cash provided by (used in) financing activities	260,644	(159,709)
Net increase (decrease) in cash and cash equivalents	11,353	(188,682)
Cash and cash equivalents, beginning of period	360,396	524,611
Cash and cash equivalents, end of period	371,749	335,929
Supplemental disclosure of cash flow information
Cash payments for interest	29,251	20,348
Cash payments for income taxes	23,980	37,350
Supplemental disclosure of noncash investing and financing activities
Loans transferred to repossessed properties	$ (11,005)	$ (1,221)

Nature of Operations and Summar

Nature of Operations and Summary of Significant Policies	6 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Nature of Operations and Summary of Significant Policies	Nature of Operations and Summary of Significant Policies Nature of Operations Great Western Bancorp, Inc. (the “Company”) is a bank holding company organized under the laws of Delaware and is listed on the New York Stock Exchange ("NYSE") under the symbol GWB. 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 agri-business banking in Arizona, Colorado, Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota 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. Basis of Presentation 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. Certain previously reported amounts have been reclassified to conform to the current presentation. The unaudited interim consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements for the year ended September 30, 2017 , 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 on the consolidated financial statements and accompanying notes. Actual results could differ from these estimates. Subsequent Events The Company has evaluated all events or transactions that occurred through the date the Company issued these financial statements. Other than those events described below, there were no other material events that would require recognition in the consolidated financial statements or disclosure in the notes to the consolidated financial statements. On April 26, 2018 , the Board of Directors of the Company declared a dividend of $0.25 per common share payable on May 23, 2018 to stockholders of record as of close of business on May 11, 2018 . Correction of Prior Period Balances The consolidated statements of income for the quarter ended March 31, 2017 have been revised to correct an immaterial classification error in interest income and noninterest income related to credit card interchange income. As a result, the consolidated statements of income have been revised to reflect these changes as follows. As originally reported Adjustments As revised (dollars in thousands) Three months ended March 31, 2017 Interest income - loans $ 101,136 $ (1,655 ) $ 99,481 Noninterest income - service charges and other fees 11,919 1,655 13,574 Six months ended March 31, 2017 Interest income - loans $ 202,818 $ (3,405 ) $ 199,413 Noninterest income - service charges and other fees 24,005 3,405 27,410 As originally reported Adjustments As revised (dollars in thousands) Twelve months ended September 30, 2017 Interest income - loans $ 414,434 $ (7,152 ) $ 407,282 Noninterest income - service charges and other fees 48,573 7,152 55,725 Twelve months ended September 30, 2016 Interest income - loans $ 370,444 $ (6,716 ) $ 363,728 Noninterest income - service charges and other fees 46,209 6,716 52,925 The above revisions had no effect on net income, earnings per share, retained earnings or capital ratios. Periods not presented herein will be revised, as applicable, as they are included in future filings.

New Accounting Pronouncements

New Accounting Pronouncements	6 Months Ended
	Mar. 31, 2018
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements	New Accounting Pronouncements In February 2018, the Financial Accounting Standards Board ("FASB") issued ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allows for the reclassification of stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017 ("Tax Reform Act") from other comprehensive income to retained earnings. ASU 2018-02 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. The Company early adopted ASU 2018-02 during the second quarter of fiscal year 2018 with period of adoption application. Upon adoption, the Company made a policy election to reclassify stranded tax effects of approximately $2.4 million from accumulated other comprehensive income to retained earnings. In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities , which amends the hedge accounting recognition and presentation requirements in ASC 815 to improve the transparency and understandability of information conveyed to financial statement users about an entity’s risk management activities to better align the entity’s financial reporting for hedging relationships with those risk management activities and to reduce the complexity of and simplify the application of hedge accounting. ASU 2017-12 is to be applied to all existing hedging relationships on the date of adoption and will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted in any interim period, with the effect of adoption reflected as of the beginning of the fiscal year of adoption. The Company is currently evaluating the potential impact of ASU 2017-12 on our consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which addresses timelier recording of credit losses on loans and other financial instruments held by financial institutions and other organizations. ASU 2016-13 requires institutions to measure all expected credit losses related to financial assets measured at amortized costs with an expected loss model based on historical experience, current conditions and reasonable and supportable forecasts relevant to affect the collectability of the financial assets, which is referred to as the current expected credit loss (CECL) model. ASU 2016-13 requires enhanced disclosures, including qualitative and quantitative requirements, to help understand significant estimates and judgments used in estimating credit losses, as well as provide additional information about the amounts recorded in the financial statements. ASU 2016-13 will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019, with early adoption permitted after December 15, 2018. The amendment requires the use of the modified retrospective approach for adoption. The Company has formed a project team to work on the implementation of ASU 2016-13 and is currently evaluating the potential impact on our consolidated financial statements. In February 2016, the FASB issued ASU 2016-02 , Leases (Topic 842) , which requires that lessees recognize the assets and liabilities arising from leases on the balance sheet and disclosing key information about leasing arrangements. Lessees will be required to recognize an obligation for future lease payments measured on a discounted basis and a related right-of-use asset. ASU 2016-02 does not significantly change lease accounting requirements applicable to lessors; however, certain changes were made to align, where necessary, lessor accounting with the lessee accounting model and ASC Topic 606, "Revenue from Contracts with Customers." ASU 2016-02 will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. The Company is currently evaluating the potential impact of ASU 2016-02 on our consolidated financial statements. In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10) - Recognition and Measurement of Financial Assets and Financial Liabilities , which requires equity investments, in general, to be measured at fair value with changes in fair value recognized in earnings. It also eliminates the requirement to disclose the methods and significant assumptions used to estimate the fair value for financial instruments measured at amortized cost, requires entities to use the exit price notion when measuring fair value, requires an entity to present separately in other comprehensive income the portion of the total change in fair value of a liability resulting from a change in the measurement category and form on the balance sheet or accompanying notes, clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available for sale securities in combination with the entity's other deferred tax assets, and simplifies the impairment assessment of equity investments without readily determinable fair values. ASU 2016-01 will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017, with early adoption permitted. The Company does not believe ASU 2016-01 will have a material impact on our consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which implements a more robust framework that clarifies the principles for recognizing revenue and gives greater consistency and comparability in revenue recognition practices. In the new framework, an entity recognizes revenue in an amount that reflects the consideration to which the entity expects to be entitled in exchange for goods or services. The new model requires the identification of performance obligations included in the contract with customers, a determination of the transaction price and an allocation of the price to those performance obligations. The entity recognizes revenue when performance obligations are satisfied. In August 2015, the FASB issued ASU 2015-14, which deferred the effective date of ASU 2014-09 to annual reporting periods beginning after December 15, 2017. In March 2016, the FASB issued ASU 2016-08, which intends to improve the operability and understandability of the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, which clarifies guidance pertaining to the identification of performance obligations and the licensing implementation. In May 2016, the FASB issued ASU 2016-11 and 2016-12, which further clarify guidance and provide practical expedients related to the adoption of ASU 2014-09. The standard permits the use of either the retrospective or cumulative effect transition method. The standard, along with subsequent guidance from FASB, lists several items that are specifically out of scope for ASU 2014-09, including but not limited to core interest income, derivative instruments, investments, and loan origination fees. To address the new standard, the Company formed a working group and has completed the initial scoping phase to determine which revenue streams may be subject to accounting or disclosure changes upon adoption in October of 2018. Subsequent to this initial scoping, the Company selected a representative sample of contracts from the in-scope revenue streams for review under the amended guidance ("key contracts"). The review of key contracts is in process. Based on this preliminary analysis, we do not anticipate significant changes as a result of implementing the standard, but will conclude on the quantitative and qualitative impacts once we have completed our review of key contracts for any in-scope items over the coming months.

Securities Available for Sale

Securities Available for Sale	6 Months Ended
	Mar. 31, 2018
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. Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated (dollars in thousands) As of March 31, 2018 U.S. Treasury securities $ 178,563 $ — $ (1,144 ) $ 177,419 Mortgage-backed securities: Government National Mortgage Association 452,297 47 (13,971 ) 438,373 Federal Home Loan Mortgage Corporation 218,838 3 (4,878 ) 213,963 Federal National Mortgage Association 179,268 — (4,591 ) 174,677 Small Business Assistance Program 237,156 144 (4,036 ) 233,264 States and political subdivision securities 70,513 10 (1,623 ) 68,900 Other 1,006 — (4 ) 1,002 Total $ 1,337,641 $ 204 $ (30,247 ) $ 1,307,598 Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated (dollars in thousands) As of September 30, 2017 U.S. Treasury securities $ 228,039 $ 579 $ (15 ) $ 228,603 Mortgage-backed securities: Government National Mortgage Association 511,457 228 (6,635 ) 505,050 Federal Home Loan Mortgage Corporation 169,147 75 (1,247 ) 167,975 Federal National Mortgage Association 170,247 22 (1,287 ) 168,982 Small Business Assistance Program 224,005 726 (1,001 ) 223,730 States and political subdivision securities 73,041 187 (642 ) 72,586 Other 1,006 28 — 1,034 Total $ 1,376,942 $ 1,845 $ (10,827 ) $ 1,367,960 The amortized cost and approximate fair value of debt securities available for sale as of March 31, 2018 and September 30, 2017 , 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 penalty. March 31, 2018 September 30, 2017 Amortized Estimated Amortized Estimated (dollars in thousands) Due in one year or less $ 43,291 $ 43,204 $ 91,535 $ 91,597 Due after one year through five years 189,787 187,741 193,117 193,373 Due after five years through ten years 15,876 15,252 16,306 16,097 Due after ten years 122 122 122 122 249,076 246,319 301,080 301,189 Mortgage-backed securities 1,087,559 1,060,277 1,074,856 1,065,737 Securities without contractual maturities 1,006 1,002 1,006 1,034 Total $ 1,337,641 $ 1,307,598 $ 1,376,942 $ 1,367,960 Proceeds from sales of securities available for sale were $25.0 million and $25.2 million for the three and six months ended March 31, 2018 and $5.0 million for both the three and six months ended March 31, 2017 , respectively. Negligible gross gains (pre-tax) or gross losses (pre-tax) were realized on the sales for the three and six months ended March 31, 2018 and 2017 using the specific identification method. The Company recognized no other-than-temporary impairment for the three and six months ended March 31, 2018 and 2017 . Securities with an estimated fair value of approximately $920.6 million and $951.4 million at March 31, 2018 and September 30, 2017 , 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 97% and 68% of the Company’s investment portfolio at estimated fair value at March 31, 2018 and September 30, 2017 , 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 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, 2018 or September 30, 2017 . 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. Less than 12 months 12 months or more Total Estimated Unrealized Estimated Unrealized Estimated Unrealized (dollars in thousands) As of March 31, 2018 U.S. Treasury securities $ 148,360 $ (873 ) $ 29,059 $ (271 ) $ 177,419 $ (1,144 ) Mortgage-backed securities 314,049 (4,765 ) 712,510 (22,711 ) 1,026,559 (27,476 ) States and political subdivision securities 14,967 (109 ) 49,249 (1,514 ) 64,216 (1,623 ) Other 1,002 (4 ) — — 1,002 (4 ) Total $ 478,378 $ (5,751 ) $ 790,818 $ (24,496 ) $ 1,269,196 $ (30,247 ) Less than 12 months 12 months or more Total Estimated Unrealized Estimated Unrealized Estimated Unrealized (dollars in thousands) As of September 30, 2017 U.S. Treasury securities $ 10,003 $ (15 ) $ — $ — $ 10,003 $ (15 ) Mortgage-backed securities 635,969 (5,425 ) 241,368 (4,746 ) 877,337 (10,171 ) States and political subdivision securities 21,705 (197 ) 25,773 (444 ) 47,478 (641 ) Other — — — — — — Total $ 667,677 $ (5,637 ) $ 267,141 $ (5,190 ) $ 934,818 $ (10,827 ) As of March 31, 2018 and September 30, 2017 , the Company had 352 and 249 securities, respectively, in an unrealized loss position.

Loans

Loans	6 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Loans	Loans The composition of loans as of March 31, 2018 and September 30, 2017 , is as follows. March 31, 2018 September 30, 2017 (dollars in thousands) Commercial real estate $ 4,467,778 $ 4,124,805 Agriculture 2,177,020 2,122,138 Commercial non-real estate 1,767,587 1,718,914 Residential real estate 866,982 932,892 Consumer 55,190 66,559 Other 41,816 43,207 Ending balance 9,376,373 9,008,515 Less: Unamortized discount on acquired loans (23,501 ) (29,121 ) Unearned net deferred fees and costs and loans in process (14,566 ) (10,841 ) Total $ 9,338,306 $ 8,968,553 The loan segments above include loans covered by a FDIC loss sharing agreement totaling $50.7 million and $57.5 million as of March 31, 2018 and September 30, 2017 , respectively, residential real estate loans held for sale totaling $2.4 million and $7.5 million at March 31, 2018 and September 30, 2017 , respectively, and $921.0 million and $1.02 billion of loans accounted for at fair value at March 31, 2018 and September 30, 2017 , respectively. Unearned net deferred fees and costs totaled $13.1 million and $11.6 million as of March 31, 2018 and September 30, 2017 , 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 $1.5 million and $(0.8) million at March 31, 2018 and September 30, 2017 , respectively. Loans guaranteed by agencies of the U.S. government totaled $170.3 million and $168.3 million at March 31, 2018 and September 30, 2017 , respectively. Principal balances of residential real estate loans sold totaled $67.6 million and $53.4 million for the three months ended March 31, 2018 and 2017 , respectively, and $117.8 million and $145.1 million for the six months ended March 31, 2018 and 2017 , respectively. Nonaccrual Interest income on loans is accrued daily on the outstanding balances. Accrual of interest is discontinued when management believes, after considering collection efforts and other factors, the borrower’s financial condition is such that collection of interest is doubtful, which is usually at 90 days past due. Generally, when loans are placed on nonaccrual status, interest receivable is reversed against interest income in the current period. Interest payments received thereafter are applied as a reduction to the remaining principal balance as long as concern exists as to the ultimate collection of the principal. Loans are removed from nonaccrual status when they become current as to both principal and interest and concern no longer exists as to the collectability of principal and interest. The following table presents the Company’s nonaccrual loans at March 31, 2018 and September 30, 2017 , excluding ASC 310-30 loans. Loans greater than 90 days past due and still accruing interest as of March 31, 2018 and September 30, 2017 , were $0.9 million and $1.9 million , respectively. March 31, 2018 September 30, 2017 (dollars in thousands) Nonaccrual loans Commercial real estate $ 26,343 $ 14,693 Agriculture 86,758 99,325 Commercial non-real estate 10,146 13,674 Residential real estate 4,058 4,421 Consumer 88 112 Total $ 127,393 $ 132,225 Credit Quality Information The Company assigns all non-consumer loans a credit quality risk rating. These ratings are Pass, Watch, Substandard, Doubtful, and Loss. Loans with a Pass and Watch rating represent those loans not classified on the Company’s rating scale for problem credits, with loans with a Watch rating being monitored and updated at least quarterly by management. Substandard loans are those where a well-defined weakness has been identified that may put full collection of contractual debt at risk. Doubtful loans are those where a well-defined weakness has been identified and a loss of contractual debt is probable. Substandard and doubtful loans are monitored and updated monthly. All loan risk ratings are updated and monitored on a continuous basis. The Company generally does not risk rate consumer loans unless a default event such as bankruptcy or extended nonperformance takes place. Alternatively, standard credit scoring systems are used to assess credit risks of consumer loans. The following table presents the composition of the loan portfolio by internally assigned grade as of March 31, 2018 and September 30, 2017 . 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 $921.0 million at March 31, 2018 and $1.02 billion at September 30, 2017 . As of March 31, 2018 Commercial Real Estate Agriculture Commercial Residential Real Estate Consumer Other Total (dollars in thousands) Credit Risk Profile by Internally Assigned Grade Grade: Pass $ 3,888,128 $ 1,683,280 $ 1,443,731 $ 798,778 $ 54,324 $ 41,816 $ 7,910,057 Watchlist 62,695 152,878 33,852 4,935 326 — 254,686 Substandard 62,784 123,714 19,552 7,152 235 — 213,437 Doubtful 113 5 2,756 126 — — 3,000 Loss — — — — — — — Ending balance 4,013,720 1,959,877 1,499,891 810,991 54,885 41,816 8,381,180 Loans covered by a FDIC loss sharing agreement — — — 50,727 — — 50,727 Total $ 4,013,720 $ 1,959,877 $ 1,499,891 $ 861,718 $ 54,885 $ 41,816 $ 8,431,907 As of September 30, 2017 Commercial Real Estate Agriculture Commercial Residential Real Estate Consumer Other Total (dollars in thousands) Credit Risk Profile by Internally Assigned Grade Grade: Pass $ 3,519,689 $ 1,577,403 $ 1,369,803 $ 853,266 $ 65,673 $ 43,207 $ 7,429,041 Watchlist 80,195 157,407 31,878 4,158 187 — 273,825 Substandard 37,627 130,953 21,438 7,368 306 — 197,692 Doubtful 521 119 3,841 242 — — 4,723 Loss — — — — — — — Ending balance 3,638,032 1,865,882 1,426,960 865,034 66,166 43,207 7,905,281 Loans covered by a FDIC loss sharing agreement — — — 57,537 — — 57,537 Total $ 3,638,032 $ 1,865,882 $ 1,426,960 $ 922,571 $ 66,166 $ 43,207 $ 7,962,818 Past Due Loans The following table presents the Company’s past due loans at March 31, 2018 and September 30, 2017 . 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 $921.0 million at March 31, 2018 and $1.02 billion at September 30, 2017 . 30-59 Days Past Due 60-89 Days Past Due 90 Days or Greater Past Due Total Current Total Financing Receivables (dollars in thousands) As of March 31, 2018 Commercial real estate $ 3,308 $ 67 $ 22,319 $ 25,694 $ 3,988,026 $ 4,013,720 Agriculture 2,387 371 26,498 29,256 1,930,621 1,959,877 Commercial non-real estate 3,665 1,190 5,223 10,078 1,489,813 1,499,891 Residential real estate 2,568 90 1,364 4,022 806,969 810,991 Consumer 140 3 44 187 54,698 54,885 Other — — — — 41,816 41,816 Ending balance 12,068 1,721 55,448 69,237 8,311,943 8,381,180 Loans covered by a FDIC loss sharing agreement 1,283 217 588 2,088 48,639 50,727 Total $ 13,351 $ 1,938 $ 56,036 $ 71,325 $ 8,360,582 $ 8,431,907 30-59 Days Past Due 60-89 Days Past Due 90 Days or Greater Past Due Total Current Total Financing Receivables (dollars in thousands) As of September 30, 2017 Commercial real estate $ 876 $ 22,536 $ 6,504 $ 29,916 $ 3,608,116 $ 3,638,032 Agriculture 1,453 3,181 20,844 25,478 1,840,404 1,865,882 Commercial non-real estate 2,485 115 8,580 11,180 1,415,780 1,426,960 Residential real estate 1,428 76 951 2,455 862,579 865,034 Consumer 71 24 18 113 66,053 66,166 Other — — — — 43,207 43,207 Ending balance 6,313 25,932 36,897 69,142 7,836,139 7,905,281 Loans covered by a FDIC loss sharing agreement 998 54 738 1,790 55,747 57,537 Total $ 7,311 $ 25,986 $ 37,635 $ 70,932 $ 7,891,886 $ 7,962,818 Impaired Loans The following table presents the Company’s impaired loans. This table excludes purchased credit impaired loans and loans measured at fair value with changes in fair value reported in earnings of $921.0 million at March 31, 2018 and $1.02 billion at September 30, 2017 . March 31, 2018 September 30, 2017 Recorded Investment Unpaid Principal Balance Related Allowance Recorded Investment Unpaid Principal Balance Related Allowance (dollars in thousands) Impaired loans: With an allowance recorded: Commercial real estate $ 48,532 $ 49,799 $ 7,248 $ 20,819 $ 24,893 $ 3,621 Agriculture 63,293 73,823 10,465 79,219 88,268 11,468 Commercial non-real estate 14,747 18,140 4,320 17,950 28,755 4,779 Residential real estate 5,208 5,991 2,549 5,177 5,874 2,581 Consumer 217 225 74 280 287 86 Total impaired loans with an allowance recorded 131,997 147,978 24,656 123,445 148,077 22,535 With no allowance recorded: Commercial real estate 13,335 52,866 — 16,652 69,677 — Agriculture 61,643 66,567 — 51,256 64,177 — Commercial non-real estate 14,110 23,372 — 13,983 38,924 — Residential real estate 2,166 5,157 — 2,574 9,613 — Consumer 14 133 — 13 950 — Total impaired loans with no allowance recorded 91,268 148,095 — 84,478 183,341 — Total impaired loans $ 223,265 $ 296,073 $ 24,656 $ 207,923 $ 331,418 $ 22,535 The following table presents the average recorded investment on impaired loans and interest income recognized on impaired loans for the three and six months ended March 31, 2018 and 2017 , respectively, are as follows. Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Average Recorded Investment Interest Income Recognized While on Impaired Status Average Recorded Investment Interest Income Recognized While on Impaired Status Average Recorded Investment Interest Income Recognized While on Impaired Status Average Recorded Investment Interest Income Recognized While on Impaired Status (dollars in thousands) Commercial real estate $ 66,577 $ 477 $ 44,807 $ 545 $ 56,875 $ 2,053 $ 47,873 $ 1,215 Agriculture 121,062 1,189 128,919 1,326 124,200 2,171 119,892 3,193 Commercial non-real estate 30,350 325 46,304 358 30,878 776 47,477 780 Residential real estate 7,578 116 9,565 126 7,636 281 9,831 240 Consumer 238 4 389 12 256 8 391 27 Total $ 225,805 $ 2,111 $ 229,984 $ 2,367 $ 219,845 $ 5,289 $ 225,464 $ 5,455 Valuation adjustments made to repossessed properties totaled $0.7 million and $0.5 million for the three months ended March 31, 2018 and 2017 and $0.7 million and $0.9 million for the six months ended March 31, 2018 and 2017 , respectively. The adjustments are included in noninterest expense. Troubled Debt Restructurings 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 credit 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 and lease losses for TDRs were $10.0 million and $8.8 million at March 31, 2018 and September 30, 2017 , respectively. There were $0.7 million commitments to lend additional funds to borrowers whose loans were modified in a TDR as of March 31, 2018 and no commitments to lend additional funds to borrowers whose loans were modified in a TDR as of September 30, 2017 . The following table presents the recorded value of the Company’s TDR balances as of March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 Accruing Nonaccrual Accruing Nonaccrual (dollars in thousands) Commercial real estate $ 617 $ 2,632 $ 1,121 $ 5,351 Agriculture 29,200 60,098 22,678 59,633 Commercial non real estate 7,647 3,916 8,369 5,641 Real estate 249 739 311 688 Consumer 83 — 11 21 Total $ 37,796 $ 67,385 $ 32,490 $ 71,334 The following table presents a summary of all accruing loans restructured in TDRs during the three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Recorded Investment Recorded Investment Number Pre-Modification Post-Modification Number Pre-Modification Post-Modification (dollars in thousands) Commercial real estate Rate modification — $ — $ — — $ — $ — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial real estate — — — — — — Agriculture Rate modification 1 5,500 5,500 — — — Term extension — — — 2 8,434 8,434 Payment modification 1 573 573 — — — Bankruptcy — — — — — — Other — — — — — — Total agriculture 2 6,073 6,073 2 8,434 8,434 Commercial non-real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — 2 93 93 Bankruptcy — — — — — — Other — — — — — — Total commercial non-real estate — — — 2 93 93 Residential real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total residential real estate — — — — — — Consumer Rate modification 1 73 73 — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total consumer 1 73 73 — — — Total accruing 3 $ 6,146 $ 6,146 4 $ 8,527 $ 8,527 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 accruing loans restructured in TDRs during the six months ended March 31, 2018 and 2017 . Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Recorded Investment Recorded Investment Number Pre-Modification Post-Modification Number Pre-Modification Post-Modification (dollars in thousands) Commercial real estate Rate modification — $ — $ — — $ — $ — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial real estate — — — — — — Agriculture Rate modification 1 5,500 5,500 — — — Term extension — — — 2 8,434 8,434 Payment modification 1 573 573 — — — Bankruptcy — — — — — — Other — — — — — — Total agriculture 2 6,073 6,073 2 8,434 8,434 Commercial non-real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — 4 526 526 Bankruptcy — — — — — — Other — — — — — — Total commercial non-real estate — — — 4 526 526 Residential real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — 1 9 9 Bankruptcy — — — — — — Other — — — — — — Total residential real estate — — — 1 9 9 Consumer Rate modification 1 73 73 — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total consumer 1 73 73 — — — Total accruing 3 $ 6,146 $ 6,146 7 $ 8,969 $ 8,969 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 three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Recorded Investment Recorded Investment Number Pre-Modification Post-Modification Number Pre-Modification Post-Modification (dollars in thousands) Commercial real estate Rate modification — $ — $ — — $ — $ — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial real estate — — — — — — Agriculture Rate modification — — — — — — Term extension 3 6,324 6,324 6 12,988 12,988 Payment modification 3 2,050 2,050 — — — Bankruptcy — — — — — — Other — — — — — — Total agriculture 6 8,374 8,374 6 12,988 12,988 Commercial non-real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial non-real estate — — — — — — Residential real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total residential real estate — — — — — — Consumer Rate modification — — — — — — Term extension — — — 3 21 21 Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total consumer — — — 3 21 21 Total non-accruing 6 $ 8,374 $ 8,374 9 $ 13,009 $ 13,009 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, 2018 and 2017 . Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Recorded Investment Recorded Investment Number Pre-Modification Post-Modification Number Pre-Modification Post-Modification (dollars in thousands) Commercial real estate Rate modification — $ — $ — — $ — $ — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial real estate — — — — — — Agriculture Rate modification — — — — — — Term extension 3 6,324 6,324 6 12,988 12,988 Payment modification 3 2,050 2,050 — — — Bankruptcy — — — — — — Other — — — — — — Total agriculture 6 8,374 8,374 6 12,988 12,988 Commercial non-real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial non-real estate — — — — — — Residential real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — 1 21 21 Bankruptcy — — — — — — Other — — — — — — Total residential real estate — — — 1 21 21 Consumer Rate modification — — — — — — Term extension — — — 3 21 21 Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total consumer — — — 3 21 21 Total non-accruing 6 $ 8,374 $ 8,374 10 $ 13,030 $ 13,030 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 loans that were modified as TDRs within the previous 12 months and for which there was a payment default for the three and six months ended March 31, 2018 and 2017 , respectively. Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment (dollars in thousands) Commercial real estate — $ — — $ — 1 $ 1,012 1 $ 34 Agriculture 3 4,264 — — 4 5,011 — — Commercial non-real estate — — 1 — — — 1 — Residential real estate — — — — — — — — Consumer — — — — — — — — Total 3 $ 4,264 1 $ — 5 $ 6,023 2 $ 34 A loan is considered to be in payment default once it is 90 days or more contractually past due under the modified terms. The table above includes loans that experienced a payment default during the period, but may be performing in accordance with the modified terms as of the balance sheet date. For the three months ended March 31, 2018 and 2017 , there were $0.1 million and $2.1 million , respectively, and $0.6 million and $2.1 million for the six months ended March 31, 2018 and 2017 , respectively, of loans removed from TDR status as they were restructured at market terms and are performing.

Allowance for Loan and Lease Lo

Allowance for Loan and Lease Losses	6 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Allowance for Loan and Lease Losses	Allowance for Loan and Lease Losses The allowance for loan and lease losses is determined based on an ongoing evaluation, driven primarily by monitoring changes in loan risk grades, delinquencies, and other credit risk indicators, which are inherently subjective. The Company considers the uncertainty related to certain industry sectors and the extent of credit exposure to specific borrowers within the portfolio. In addition, consideration is given to concentration risks associated with the various loan portfolios and current economic conditions that might impact the portfolio. The Company also considers changes, if any, in underwriting activities, the loan portfolio composition (including product mix and geographic, industry, or customer-specific concentrations), trends in loan performance, the level of allowance coverage relative to similar banking institutions and macroeconomic factors, such as changes in unemployment rates, gross domestic product, and consumer bankruptcy filings. Changes to the allowance for loan and lease losses are made by charges to the provision for loan and lease losses, which is reflected on the consolidated statements of income. Past due status is monitored as an indicator of credit deterioration. Loans that are 90 days or more past due are put on nonaccrual status unless a repayment is eminent. Loans deemed to be uncollectible are charged off against the allowance for loan and lease losses. Recoveries of amounts previously charged-off are credited to the allowance for loan and lease losses. The allowance for loan and lease losses consist of reserves for probable losses that have been identified related to specific borrowing relationships that are individually evaluated for impairment (“specific reserve”), as well as probable losses inherent in our loan portfolio that are not specifically identified (“collective reserve”). The specific reserve relates to impaired loans. A loan is impaired when, based on current information and events, it is probable the Company will be unable to collect all amounts due (interest as well as principal) according to the contractual terms of the loan agreement. Specific reserves are determined on a loan-by-loan basis based on management’s best estimate of the Company's exposure, given the current payment status of the loan, the present value of expected payments, and the value of any underlying collateral. Impaired loans also include loans modified in troubled debt restructurings. Generally, the impairment related to troubled debt restructurings is measured based on the fair value of the collateral, less cost to sell, or the present value of expected payments relative to the unpaid principal balance. If the impaired loan is identified as collateral dependent, then the fair value of the collateral method of measuring the amount of the impairment is utilized. This method requires obtaining an independent appraisal of the collateral and reducing the appraised value by applying a discount factor to the appraised value, if necessary, and including costs to sell. Management’s estimate for collective reserves reflects losses incurred in the loan portfolio as of the consolidated balance sheet reporting date. Incurred loss estimates primarily are based on historical loss experience and portfolio mix. Incurred loss estimates may be adjusted for qualitative factors such as current economic conditions and current portfolio trends including credit quality, concentrations, aging of the portfolio, and/or significant policy and underwriting changes. The following tables present the Company’s allowance for loan and lease losses roll forward for the three and six months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Beginning balance January 1, 2018 $ 15,995 $ 24,750 $ 16,434 $ 5,475 $ 307 $ 1,062 $ 64,023 Charge-offs (1,268 ) (783 ) (1,605 ) (20 ) (62 ) (557 ) (4,295 ) Recoveries 61 125 88 27 20 190 511 Provision 4,077 152 813 (341 ) 14 281 4,996 Impairment (improvement) of ASC 310-30 loans 49 (115 ) — (30 ) — — (96 ) Ending balance March 31, 2018 $ 18,914 $ 24,129 $ 15,730 $ 5,111 $ 279 $ 976 $ 65,139 Three Months Ended March 31, 2017 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Beginning balance January 1, 2017 $ 16,623 $ 28,519 $ 13,443 $ 6,786 $ 340 $ 1,056 $ 66,767 Charge-offs (1,824 ) (4,554 ) (1,734 ) (117 ) (31 ) (819 ) (9,079 ) Recoveries 286 118 121 56 15 392 988 Provision 2,096 2,237 119 210 47 351 5,060 (Improvement) of ASC 310-30 loans (185 ) — — (866 ) — — (1,051 ) Ending balance March 31, 2017 $ 16,996 $ 26,320 $ 11,949 $ 6,069 $ 371 $ 980 $ 62,685 Six Months Ended March 31, 2018 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Beginning balance October 1, 2017 $ 16,941 $ 25,757 $ 14,114 $ 5,347 $ 329 $ 1,015 $ 63,503 Charge-offs (1,597 ) (2,981 ) (2,844 ) (275 ) (116 ) (1,091 ) (8,904 ) Recoveries 209 172 209 117 42 334 1,083 Provision 3,322 1,296 4,251 (11 ) 24 718 9,600 Impairment (improvement) of ASC 310-30 loans 39 (115 ) — (67 ) — — (143 ) Ending balance March 31, 2018 $ 18,914 $ 24,129 $ 15,730 $ 5,111 $ 279 $ 976 $ 65,139 Six Months Ended March 31, 2017 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Beginning balance October 1, 2016 $ 17,946 $ 25,115 $ 12,990 $ 7,106 $ 438 $ 1,047 $ 64,642 Charge-offs (1,824 ) (7,420 ) (3,693 ) (267 ) (110 ) (1,317 ) (14,631 ) Recoveries 385 144 219 262 30 576 1,616 Provision 549 8,481 2,433 (140 ) 13 674 12,010 (Improvement) of ASC 310-30 loans (60 ) — — (892 ) — — (952 ) Ending balance March 31, 2017 $ 16,996 $ 26,320 $ 11,949 $ 6,069 $ 371 $ 980 $ 62,685 The following tables provide details regarding the allowance for loan and lease losses and balance by type of allowance as of March 31, 2018 and September 30, 2017 . These tables are presented net of unamortized discount on acquired loans and excludes loans of $921.0 million measured at fair value, loans held for sale of $2.4 million , and guaranteed loans of $161.5 million for March 31, 2018 and loans measured at fair value of $1.02 billion , loans held for sale of $7.5 million , and guaranteed loans of $168.3 million for September 30, 2017 . As of March 31, 2018 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Allowance for loan and lease losses Individually evaluated for impairment $ 7,248 $ 10,465 $ 4,320 $ 2,549 $ 74 $ — $ 24,656 Collectively evaluated for impairment 10,950 13,664 11,410 2,444 205 976 39,649 ASC 310-30 loans 716 — — 118 — — 834 Total allowance $ 18,914 $ 24,129 $ 15,730 $ 5,111 $ 279 $ 976 $ 65,139 Financing Receivables Individually evaluated for impairment $ 61,867 $ 124,936 $ 28,857 $ 7,374 $ 231 $ — $ 223,265 Collectively evaluated for impairment 3,846,737 1,808,883 1,407,897 804,298 54,120 41,816 7,963,751 ASC 310-30 loans 28,494 2,746 2,231 46,945 534 — 80,950 Loans Outstanding $ 3,937,098 $ 1,936,565 $ 1,438,985 $ 858,617 $ 54,885 $ 41,816 $ 8,267,966 As of September 30, 2017 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Allowance for loan and lease losses Individually evaluated for impairment $ 3,621 $ 11,468 $ 4,779 $ 2,581 $ 86 $ — $ 22,535 Collectively evaluated for impairment 12,638 14,174 9,335 2,570 243 1,015 39,975 ASC 310-30 loans 682 115 — 196 — — 993 Total allowance $ 16,941 $ 25,757 $ 14,114 $ 5,347 $ 329 $ 1,015 $ 63,503 Financing Receivables Individually evaluated for impairment $ 37,471 $ 130,475 $ 31,933 $ 7,751 $ 293 $ — $ 207,923 Collectively evaluated for impairment 3,487,232 1,702,634 1,333,888 854,330 65,207 43,207 7,486,498 ASC 310-30 loans 30,099 7,174 1,920 52,736 666 — 92,595 Loans Outstanding $ 3,554,802 $ 1,840,283 $ 1,367,741 $ 914,817 $ 66,166 $ 43,207 $ 7,787,016 For acquired loans not accounted for under ASC 310-30 (purchased non-impaired), the Company utilizes specific and collective reserve calculation methods similar to originated loans. The required ALLL for these loans is included in the individually evaluated for impairment bucket of the ALLL if the loan is rated substandard or worse, and in the collectively evaluated for impairment bucket for pass rated loans. The Company maintains an ALLL for acquired loans accounted for under ASC 310-30 as a result of impairment to loan pools arising from the periodic re-valuation of these loans. Any impairment in the individual pool is generally recognized in the current period as provision for loan and lease losses. Any improvement in the estimated cash flows, is generally not recognized immediately, but is instead reflected as an adjustment to the related loan pools yield on a prospective basis once any previously recorded impairment has been recaptured. The ALLL for ASC 310-30 loans totaled $0.8 million at March 31, 2018 , compared to $1.0 million at September 30, 2017 . For the three and six months ended March 31, 2018 , loan pools accounted for under ASC 310-30 had a net reversal of provision of $0.1 million and $0.1 million , respectively. The net reversals of provision for the periods ended March 31, 2018 were driven by increases in expected cash flows. Net provision reversal for the three and six months ended March 31, 2017 , totaled $1.1 million and $1.0 million , respectively. The net reversals of provision for the periods ended March 31, 2017 were a result of updated assumptions being applied to one of the acquired mortgage pools which resulted in higher than expected cash flows. The reserve for unfunded loan commitments was $0.5 million at both March 31, 2018 and September 30, 2017 and is recorded in other liabilities on the consolidated balance sheets.

Accounting for Certain Loans Ac

Accounting for Certain Loans Acquired with Deteriorated Credit Quality	6 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Accounting for Certain Loans Acquired with Deteriorated Credit Quality	Accounting for Certain Loans Acquired with Deteriorated Credit Quality In June 2010 and May 2016 , the Company acquired certain loans that had deteriorated credit quality (ASC 310-30 loans or Purchased Credit Impaired loans). Several factors were considered when evaluating whether a loan was considered a purchased credit impaired loan, including the delinquency status of the loan, updated borrower credit status, geographic information and updated loan-to-values ("LTV"). Further, these purchased credit impaired loans had differences between contractual amounts owed and cash flows expected to be collected, that were at least in part, due to credit quality. U.S. GAAP allows purchasers to aggregate purchased credit 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, homogeneous 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 homogeneous loans. The re-assessment of purchased credit impaired loans resulted in the following changes in the accretable yield during the three and six months ended March 31, 2018 and 2017 . Three Months Ended Six Months Ended March 31, 2018 March 31, 2017 March 31, 2018 March 31, 2017 (dollars in thousands) Balance at beginning of period $ 41,918 $ 39,758 $ 44,131 $ 38,124 Accretion (3,664 ) (3,040 ) (7,045 ) (5,978 ) Reclassification from nonaccretable difference (413 ) 1,987 755 6,559 Balance at end of period $ 37,841 $ 38,705 $ 37,841 $ 38,705 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 credit impaired loans at March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 Outstanding Balance ¹ Recorded Investment ² Carrying Value ³ Outstanding Balance ¹ Recorded Investment ² Carrying Value ³ (dollars in thousands) Commercial real estate $ 105,489 $ 28,494 $ 27,778 $ 110,797 $ 30,099 $ 29,417 Agriculture 5,813 2,746 2,746 10,463 7,174 7,059 Commercial non-real estate 10,001 2,231 2,231 9,825 1,920 1,920 Residential real estate 55,326 46,945 46,827 61,981 52,736 52,540 Consumer 668 534 534 798 666 666 Total lending $ 177,297 $ 80,950 $ 80,116 $ 193,864 $ 92,595 $ 91,602 1 Represents the legal balance of ASC 310-30 loans. 2 Represents the book balance of ASC 310-30 loans. 3 Represents the book balance of ASC 310-30 loans net of the related allowance for loan and lease losses.

FDIC Indemnification Asset

FDIC Indemnification Asset	6 Months Ended
	Mar. 31, 2018
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 other repossessed property, 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, 2018 and 2017 . Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands) Balance at beginning of period $ 4,692 $ 9,887 $ 5,704 $ 10,777 Amortization (671 ) (1,114 ) (1,689 ) (1,981 ) Changes in expected reimbursements from FDIC for changes in expected credit losses (76 ) (133 ) (94 ) (105 ) Changes in reimbursable expenses (456 ) (299 ) (662 ) (538 ) Reimbursements of covered losses to the FDIC 189 30 419 218 Balance at end of period $ 3,678 $ 8,371 $ 3,678 $ 8,371 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 agreement. The commercial loss share agreement claim period ended on June 4, 2015 . The non-commercial loss share agreement ends June 4, 2020 .

Derivative Financial Instrument

Derivative Financial Instruments	6 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments The Company uses interest rate swaps to manage its interest rate risk and market risk in accommodating the needs of its customers. The Company recognizes all derivatives on the consolidated balance sheet at fair value in either other assets or accrued expenses and other liabilities as appropriate. The following table presents the notional amounts and gross fair values of all derivative assets and liabilities held by the Company as of March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 Notional Amount Gross Gross Notional Amount Gross Gross (dollars in thousands) Derivatives not designated as hedging instruments: Interest rate swaps Financial institution counterparties $ 1,039,100 $ 17,185 $ (6,943 ) $ 1,025,474 $ 4,967 $ (22,737 ) Customer counterparties 118,606 1,602 (1,112 ) 36,072 615 — Mortgage loan commitments 27,499 3 — 37,765 — (48 ) Mortgage loan forward sale contracts 27,398 — (3 ) 43,628 48 — Total $ 1,212,603 $ 18,790 $ (8,058 ) $ 1,142,939 $ 5,630 $ (22,785 ) Netting of Derivatives We record the derivatives on a net basis when a right of offset exists, based on transactions with a single counterparty that are subject to a legally enforceable master netting agreement. When bilateral netting agreements or similar agreements exist between the Company and its counterparties that create a single legal claim or obligation to pay or receive the net amount in settlement of the individual derivative contracts, the Company reports derivative assets and liabilities on a net by derivative contract by counterparty basis. The following tables provide information on the Company's netting adjustments as of March 31, 2018 and September 30, 2017 . Amounts offset on the Consolidated Balance Sheet Gross Fair Value Fair Value Offset Amount Cash Collateral Net Amount Presented on the Consolidated Balance Sheet (dollars in thousands) March 31, 2018 Total Derivative Assets $ 18,790 $ (6,943 ) $ (9,015 ) $ 2,832 Total Derivative Liabilities ¹ $ (8,058 ) $ 6,943 $ (3 ) $ (1,118 ) 1 In addition to the cash collateral, there were securities of $5.0 million posted as collateral for financial institution counterparties at March 31, 2018. Amounts offset on the Consolidated Balance Sheet Gross Fair Value Fair Value Offset Amount Cash Collateral Net Amount Presented on the Consolidated Balance Sheet (dollars in thousands) September 30, 2017 Total Derivative Assets $ 1,850 $ (1,850 ) $ — $ — Total Derivative Liabilities ¹ ² (19,005 ) 1,850 — (17,155 ) 1 In addition to the cash collateral, there were securities of $25.0 million posted as collateral for financial institution counterparties at September 30, 2017. 2 There was an additional $2.3 million of collateral held for initial margin with our Futures Clearing Merchant for clearing derivatives at September 30, 2017 and is included in other assets in the consolidated balance sheets. 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 are 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. Credit-risk-related contingent features The Company has agreements with its derivative counterparties that contain a provision where if the Company or the derivative counterparty fails to maintain its status as a well/adequately capitalized institution, then the other party has the right to terminate the derivative positions and the Company or the derivative counterparty would be required to settle its obligations under the agreements. The Company has minimum collateral posting thresholds with its Swap Dealers and Futures Clearing Merchant. Beginning in the second quarter of fiscal year 2018 , the Company has entered into risk participation agreements ("RPA"s) with some of its derivative counterparties to assume the credit exposure related to interest rate derivative contracts. The Company's loan customer enters into an interest rate swap directly with a derivative counterparty and the Company agrees through an RPA to take on the counterparty's risk of loss on the interest rate swap due to a default by the customer. As of March 31, 2018 , the amounts of these instruments were not material to the financial statements. The effect of derivatives on the consolidated statements of income for the three and six months ended March 31, 2018 and 2017 was as follows. Amount of Gain (Loss) Recognized in Statements of Income Three Months Ended Six Months Ended Location of Gain (Loss) Recognized in Statements of Income March 31, 2018 March 31, 2017 March 31, 2018 March 31, 2017 (dollars in thousands) Derivatives not designated as hedging instruments: Interest rate swaps Net realized and unrealized gain on derivatives $ 14,282 $ 1,592 $ 21,509 $ 60,568 Mortgage loan commitments Net realized and unrealized gain on derivatives 2 158 3 53 Mortgage loan forward sale contracts Net realized and unrealized gain on derivatives (2 ) (158 ) (3 ) (53 )

The Fair Value Option for Certa

The Fair Value Option for Certain Loans	6 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
The Fair Value Option For Certain Loans	The Fair Value Option for Certain Loans The Company has elected to measure certain long-term loans 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 18 for additional disclosures regarding the fair value of the fair value option loans. Long-term loans for which the fair value option has been elected had a net unfavorable difference between the aggregate fair value and the aggregate unpaid loan principal balance and written loan commitment amount of approximately $21.0 million at March 31, 2018 and a net favorable difference of approximately $8.8 million at September 30, 2017 . The total unpaid principal balance of these long-term loans was approximately $942.0 million and $1.01 billion at March 31, 2018 and September 30, 2017 , respectively. The fair value of these loans is included in total loans in the consolidated balance sheets and are grouped with commercial real estate, agricultural and commercial non-real estate loans in Note 4. As of March 31, 2018 and September 30, 2017 , there were loans with a fair value of $13.3 million and $14.7 million , respectively, which were greater than 90 days past due or in nonaccrual status with an unpaid principal balance of $14.8 million and $17.0 million , respectively. 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 within the consolidated statements of income are as follows for the three and six months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Noninterest Income Total Changes in Fair Value Noninterest Income Total Changes in Fair Value Noninterest Income Total Changes in Fair Value Noninterest Income Total Changes in Fair Value (dollars in thousands) Long-term loans $ (14,838 ) $ (14,838 ) $ (5,216 ) $ (5,216 ) $ (23,502 ) $ (23,502 ) $ (69,218 ) $ (69,218 ) For long-term loans, $1.4 million and $0.3 million for the three months ended March 31, 2018 and 2017 , respectively, and $0.3 million and $0.3 million for the six months ended March 31, 2018 and 2017 , 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 Intangi

Core Deposits and Other Intangibles	6 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Core Deposits and Other Intangibles	Core Deposits and Other Intangibles The following table presents a summary of intangible assets subject to amortization as of March 31, 2018 and September 30, 2017 . Core Deposit Intangible Brand Other Total (dollars in thousands) As of March 31, 2018 Gross carrying amount $ 7,339 $ 8,464 $ 538 $ 16,341 Accumulated amortization (2,116 ) (5,546 ) (157 ) (7,819 ) Net intangible assets $ 5,223 $ 2,918 $ 381 $ 8,522 As of September 30, 2017 Gross carrying amount $ 7,339 $ 8,464 $ 538 $ 16,341 Accumulated amortization (1,579 ) (5,264 ) (124 ) (6,967 ) Net intangible assets $ 5,760 $ 3,200 $ 414 $ 9,374 Amortization expense of intangible assets was $0.4 million and $0.6 million for the three months ended March 31, 2018 and 2017 , respectively, and $0.9 million and $1.4 million for the six months ended March 31, 2018 and 2017 . 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. Amount (dollars in thousands) Remaining in 2018 $ 810 2019 1,538 2020 1,430 2021 1,334 2022 1,249 2023 and thereafter 2,161 Total $ 8,522

Loan Servicing Rights

Loan Servicing Rights	6 Months Ended
	Mar. 31, 2018
Transfers and Servicing [Abstract]
Loan Servicing Rights	Loan Servicing Rights Loan servicing rights are created when residential mortgage loans are sold in the secondary market with the seller retaining the right to service those loans and receive servicing income over the life of the loan. The Company acquired loan servicing rights as a part of the HF Financial acquisition. The actual balance of loans being serviced for others are not reported as assets in the accompanying consolidated balance sheets. The following table is the activity for loan servicing rights and the related valuation allowance for the three and six months ended March 31, 2018 and 2017 . Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands) Loan servicing rights Beginning of period $ 3,842 $ 5,286 $ 4,155 $ 5,794 Additions — — — — Amortization ¹ (246 ) (380 ) (559 ) (888 ) End of period $ 3,596 $ 4,906 $ 3,596 $ 4,906 Valuation allowance Beginning of period $ (43 ) $ (8 ) $ (81 ) $ (13 ) (Additions) / reductions ¹ 33 5 71 10 End of period $ (10 ) $ (3 ) $ (10 ) $ (3 ) Loan servicing rights, net $ 3,586 $ 4,903 $ 3,586 $ 4,903 Servicing fees received $ 435 $ 525 $ 872 $ 1,073 Balance of loans serviced at: Beginning of period 692,593 823,375 722,461 868,865 End of period 669,767 792,779 669,767 792,779 1 Changes to carrying amounts are reported net of loan servicing income on the consolidated statements of comprehensive income for the periods presented. Amortization of servicing rights is adjusted each quarter based upon analysis of portfolio attributes and factors, including an evaluation of historical prepayment activity and prospective industry consensus data. An independent third party is utilized to calculate the amortization and valuation based upon specific loan characteristics, prepayment speeds generated from a validation model utilizing both empirical and market derived data and discount rates. At March 31, 2018 , the constant prepayment rates (CPR) used to calculate the amortization averaged 10.4% . For valuation purposes, an average discount rate of 11.9% was utilized at March 31, 2018 . Based on the Company's analysis of mortgage servicing rights, a negligible valuation reserve was recorded at March 31, 2018 , and a $0.1 million valuation reserve was recorded at September 30, 2017 .

Securities Sold Under Agreement

Securities Sold Under Agreements to Repurchase	6 Months Ended
	Mar. 31, 2018
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 overnight following the transaction date. Securities underlying the agreements had an amortized cost of approximately $131.2 million and $139.3 million and fair value of approximately $126.7 million and $137.4 million at March 31, 2018 and September 30, 2017 , respectively. In most cases, the Company over-collateralizes the repurchase agreements at 102% of total funds borrowed to protect the purchaser from changes in market value. Additionally, the Company utilizes held-in-custody procedures to ensure the securities sold under repurchase agreements are unencumbered. The following tables present the gross obligation by the class of collateral pledged and the remaining contractual maturity of the agreements at March 31, 2018 and September 30, 2017 . March 31, 2018 Remaining Contractual Maturity of the Agreements Overnight and Continuous Up to 30 Days 30-90 Days Greater than 90 Days Total (dollars in thousands) Repurchase agreements Municipal securities $ 3,024 $ — $ — $ — $ 3,024 Mortgage-backed securities 100,267 — — — 100,267 Total repurchase agreements $ 103,291 $ — $ — $ — $ 103,291 September 30, 2017 Remaining Contractual Maturity of the Agreements Overnight and Continuous Up to 30 Days 30-90 Days Greater than 90 Days Total (dollars in thousands) Repurchase agreements Municipal securities $ 3,626 $ — $ — $ — $ 3,626 Mortgage-backed securities 129,010 — — — 129,010 Total repurchase agreements $ 132,636 $ — $ — $ — $ 132,636

FHLB Advances and Other Borrowi

FHLB Advances and Other Borrowings	6 Months Ended
	Mar. 31, 2018
Federal Home Loan Banks [Abstract]
FHLB Advances and Other Borrowings	FHLB Advances and Other Borrowings FHLB advances and other borrowings consist of the following at March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 (dollars in thousands) Short-term borrowings: Notes payable to FHLB, interest rates from 1.76% to 1.80% and matured dates in April 2018, collateralized by real estate loans, with various call dates at the option of the FHLB $ 350,000 $ 512,200 FHLB fed funds advance, interest rate of 1.91% and maturity date in October 2018 75,000 75,000 Long-term borrowings: Notes payable to FHLB, interest rates from 1.05% to 3.66% and maturity dates from April 2018 to July 2023, collateralized by real estate loans, with various call dates at the option of the FHLB 126,000 56,000 Total 551,000 643,200 Fair value adjustment ¹ 3 14 Total FHLB advances and other borrowings $ 551,003 $ 643,214 1 Adjustment reflects the fair value adjustments related to the FHLB advances and notes payable assumed as part of the HF Financial acquisition. The Company has a $10.0 million revolving line of credit which expires on July 28, 2018 . The line of credit has an interest rate of one month LIBOR plus 200 basis points , with interest payable monthly. There is also an unused line fee of 0 .15% on the unused portion which is payable quarterly. The interest rate was 3.88% at March 31, 2018 . There were no outstanding advances on this line of credit at March 31, 2018 and September 30, 2017 . As of March 31, 2018 and September 30, 2017 , the Company had a borrowing capacity of $1.69 billion and $1.89 billion , respectively, with the Federal Reserve Board Discount Window ("FRB Discount Window"). Principal balances of loans pledged to FRB Discount Window to collateralize the borrowing totaled $2.00 billion at March 31, 2018 and $2.55 billion at September 30, 2017 . The Company has secured this line for contingency funding. As of March 31, 2018 and September 30, 2017 , based on its collateral pledged, the additional borrowing capacity of the Company with the FHLB was $1.47 billion and $1.55 billion , respectively. Principal balances of loans pledged to the FHLB to collateralize notes payable totaled $3.75 billion and $3.71 billion at March 31, 2018 and September 30, 2017 , respectively. In second quarter of fiscal year 2018 , the Company purchased a letter of credit from the FHLB for $150.0 million which is pledged as collateral on public deposits. This letter of credit is committed until January 29, 2019 . As of March 31, 2018 , FHLB advances and other borrowings are due or callable (whichever is earlier) in subsequent fiscal years as follows. Amount (dollars in thousands) Remaining in 2018 $ 381,000 2019 75,000 2020 70,000 2021 — 2022 — 2023 and thereafter 25,000 Total $ 551,000

Subordinated Debentures and Sub

Subordinated Debentures and Subordinated Notes Payable	6 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Subordinated Debentures and Subordinated Notes Payable	Subordinated Debentures and Subordinated Notes Payable Junior Subordinated Deferrable Interest Debentures The Company has seven trusts which were created or assumed as part of prior acquisitions that as of March 31, 2018 have issued and outstanding 73,400 shares, $1,000 par value, of Company Obligated Mandatorily Redeemable Preferred Securities (the "Preferred Securities"). These seven trusts were established and exist for the sole purpose of issuing Preferred Securities and investing the proceeds in junior subordinated deferrable interest debentures (the "Debentures") issued by the Company. The Debentures constitute the sole assets of the seven trusts. The Preferred Securities provide for cumulative cash distributions calculated at a rate based on three month LIBOR plus a range from 1.48% to 3.35% adjusted quarterly. The Company may, at one or more times, defer interest payments on the Debentures for up to 20 consecutive quarters following suspension of dividends on all capital stock, but not beyond the respective maturity date. At the end of any deferral period, all accumulated and unpaid interest must be paid. The Debentures have redemption dates ranging from January 7, 2033 to October 1, 2037 ; however, the Company has the option to shorten the respective maturity date for all seven Preferred Securities as the call option date has passed. Holders of the Preferred Securities have no voting rights. The Preferred Securities are unsecured and rank junior in priority of the payment to all of the Company's indebtedness and senior to the Company's common and preferred stock. The trusts’ ability to pay amounts due on the Preferred Securities is solely dependent upon the Company making payment on the related Debentures. The Company’s obligation under the Debentures and relevant trust agreements constitute a full, irrevocable, and unconditional guarantee on a subordinated basis by it of the obligations of the trusts under the Preferred Securities. For regulatory purposes, the Debentures qualify as elements of capital. As of March 31, 2018 and September 30, 2017 , $73.6 million and $73.5 million of Debentures were eligible for treatment as Tier 1 capital, respectively. Relating to the trusts, the Company held as assets $2.5 million in common shares at March 31, 2018 and September 30, 2017 which are included in other assets on the consolidated balance sheets. Subordinated Notes Payable In 2015, the Company issued $35.0 million of 4.875% fixed-to-floating rate subordinated notes that mature on August 15, 2025 through a private placement. The notes, which qualify as Tier 2 capital under capital rules in effect at March 31, 2018 , have an interest rate of 4.875% per annum, payable semi-annually on each February 15 and August 15 , which commenced on February 15, 2016 until August 15, 2020 , to but excluding the maturity date or date of earlier redemption, the notes will bear interest at a rate per annum equal to three-month LIBOR for the related interest period plus 3.15% , payable quarterly on each November 15 , February 15 , April 15 and August 15 . The notes are subordinated in right of payment to all of the Company's senior indebtedness and effectively subordinated to all existing and future debt and all other liabilities of the Company's subsidiary bank. The Company may elect to redeem the notes (subject to regulatory approval), in whole or in part, on any early redemption date which is any interest payment date on or after August 15, 2020 at a redemption price equal to 100% of the principal amount plus any accrued and unpaid interest. Other than on an early redemption date, the notes cannot be accelerated except in the event of bankruptcy or the occurrence of certain other events of bankruptcy, insolvency or reorganization. Unamortized debt issuance costs related to these notes, which are included in Subordinated Debentures and Subordinated Notes Payable, totaled $0.2 million at March 31, 2018 and September 30, 2017 . Proceeds from the private placement of subordinated notes repaid outstanding subordinated debt. Subordinated debentures and subordinated notes payable are summarized as follows. March 31, 2018 September 30, 2017 Amount Outstanding Common Shares Held in Other Assets Amount Outstanding Common Shares Held in Other Assets (dollars in thousands) Junior subordinated debentures payable to nonconsolidated trusts GW Statutory Trust IV, variable rate of 2.85%, plus 3 month LIBOR $ 23,093 $ 693 $ 23,093 $ 693 GW Statutory Trust VI, variable rate of 1.48%, plus 3 month LIBOR 30,928 928 30,928 928 SSB Trust II, variable rate of 1.85%, plus 3 month LIBOR 2,062 62 2,062 62 HF Capital Trust III, variable rate of 3.35%, plus 3 month LIBOR 5,155 155 5,155 155 HF Capital Trust IV, variable rate of 3.10%, plus 3 month LIBOR 7,217 217 7,217 217 HF Capital Trust V, variable rate of 1.83%, plus 3 month LIBOR 5,310 310 5,310 310 HF Capital Trust VI, variable rate of 1.65%, plus 3 month LIBOR 2,155 155 2,155 155 Total junior subordinated debentures payable 75,920 $ 2,520 75,920 $ 2,520 Less: fair value adjustment ¹ (2,363 ) (2,409 ) Total junior subordinated debentures payable, net of fair value adjustment 73,557 73,511 Subordinated notes payable Fixed to floating rate, 4.875% per annum 35,000 35,000 Less: unamortized debt issuance costs (172 ) (209 ) Total subordinated notes payable 34,828 34,791 Total subordinated debentures and subordinated notes payable $ 108,385 $ 108,302 1 Adjustment reflects the fair value adjustments related to the junior subordinated deferrable interest debentures assumed as part of the HF Financial acquisition.

Income Taxes

Income Taxes	6 Months Ended
	Mar. 31, 2018
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, 2018 and 2017 . Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands) Currently paid or payable Federal $ 11,791 $ 16,789 $ 20,752 $ 29,942 State 2,939 2,337 5,394 4,701 Total 14,730 19,126 26,146 34,643 Deferred tax expense Federal 74 (1,044 ) 16,838 (566 ) State (85 ) 128 377 194 Total (11 ) (916 ) 17,215 (372 ) Total provision for income taxes $ 14,719 $ 18,210 $ 43,361 $ 34,271 The income tax provision differs from the amount of income tax determined by applying the U.S. federal income tax rate of 24.5% for the three and six months ended March 31, 2018 and 35% for the three and six months ended March 31, 2017 to pretax income due to the following. Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands) Income tax expense computed at the statutory rate $ 13,552 $ 18,679 $ 27,748 $ 37,217 Increase (decrease) in income taxes resulting from: State income taxes, net of federal benefit 2,154 1,602 4,356 3,182 Tax exempt interest income (1,415 ) (1,996 ) (2,786 ) (4,034 ) Impact of enacted federal income tax rate reduction — — 13,586 — Other 428 (75 ) 457 (2,094 ) Income tax expense, as reported $ 14,719 $ 18,210 $ 43,361 $ 34,271 Net deferred tax assets (liabilities) consist of the following components at March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 (dollars in thousands) Deferred tax assets: Allowance for loan and lease losses $ 16,311 $ 23,730 Compensation 3,246 6,227 Securities available for sale 7,406 3,413 Other real estate owned 505 763 Core deposit intangible and other fair value adjustments 4,235 6,058 Excess tax basis of FDIC indemnification asset and clawback liability 3,574 4,563 Excess tax basis of loans acquired over carrying value 5,959 9,417 Other reserves 2,810 4,406 Other 4,988 6,922 Total deferred tax assets 49,034 65,499 Deferred tax liabilities: Goodwill and other intangibles (11,518 ) (13,784 ) Premises and equipment (5,590 ) (8,828 ) Other (297 ) (487 ) Total deferred tax liabilities (17,405 ) (23,099 ) Net deferred tax assets $ 31,629 $ 42,400 At March 31, 2018 and September 30, 2017 , the Company had an income tax receivable to the Internal Revenue Service (the "IRS") of $1.3 million and $4.6 million , respectively, which is included in other liabilities on the consolidated balance sheets. 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 2014. On December 22, 2017 , the Tax Cuts and Jobs Act of 2017 (the "Tax Reform Act"), was enacted into law. Beginning in 2018 , the Tax Reform Act reduces the federal tax rate for corporations from 35% to 21% and changes or limits certain tax deductions. Because of the Company's September 30 fiscal year end, a blended statutory rate of 24.5% is applied to all net income before taxes generated during the current fiscal year. The new blended statutory rate reduced the provision for income taxes by approximately $4.8 million and $9.8 million for the three and six months ended March 31, 2018 , respectively. Another result of the lower corporate tax rate this fiscal year was the Company recording a revaluation discrete tax adjustment of $13.6 million to reduce its net deferred tax assets, which increased the provision for income taxes last quarter. The actual impact of the revaluing deferred taxes may vary from the estimated charge to provision of $13.6 million due to uncertainties in our preliminary estimates and the effect of further clarification of the new law that cannot be estimated at this time. The Company adopted new accounting guidance in the second quarter of fiscal year 2018 that allows reclassification of $2.4 million in stranded tax effects that relate to a change in the federal tax rate from accumulated other comprehensive income to retained earnings. The Bank's effective tax rate for the three and six months ended March 31, 2018 was 26.6% and 38.3% , respectively, compared to 34.1% and 32.2% for the three and six months ended March 31, 2017 , respectively. Excluding the nonrecurring deferred taxes adjustment related to federal tax reform, the three and six months ended March 31, 2018 effective tax rate was 26.6% and 26.3% , respectively. Uncertain tax positions were not significant at March 31, 2018 or September 30, 2017 .

Employee Benefit Plans

Employee Benefit Plans	6 Months Ended
	Mar. 31, 2018
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans Profit Sharing Plan The Company participates in a multiple employer 401(k) profit sharing plan ("the 401(k) 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 $1.2 million and $1.3 million to the 401(k) Plan for the three months ended March 31, 2018 and 2017 , respectively, and $3.0 million and $2.9 million for the six months ended March 31, 2018 and 2017 . Defined Benefit Plan The Company acquired a noncontributory (cash balance) defined benefit pension plan ("the Pension Plan") from HF Financial which covers former employees of HF Financial and its wholly-owned subsidiaries. Effective July 1, 2015 , the Pension Plan was frozen which eliminates future contributions for qualified individuals. On November 27, 2017 , the Company's Board of Directors voted to terminate the Pension Plan effective February 1, 2018 . In order to settle its liabilities under the Pension Plan, the Company has offered participants the option to receive either an annuity purchased from an insurance carrier or a lump-sum cash payment. If the total $2.9 million value of the Pension Plan's cash assets is insufficient to cover the lump-sum payouts and annuity purchases, the Company will contribute the necessary funds to complete the termination of the Pension Plan. In addition to plan assets, the Company has a $2.4 million pension liability recorded as of March 31, 2018 . The required final contribution is subject to a number of factors, including changes in interest rates and the exact proportion of participants electing a lump-sum distribution versus an annuity. The Company estimates that the total benefit payments will be $5.4 million as part of Pension Plan termination. At this time, the Company is unable to estimate the net income or expense associated with terminating the Pension Plan, but believes the amount will not be material to the financial statements. The Company anticipates completing the transfer of all liabilities and administrative responsibilities under the Pension Plan by the end of fiscal third quarter 2018 . Once this process is complete, the Company will no longer have any remaining pension obligations and thus no periodic pension expense.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Mar. 31, 2018
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, at that time 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. On February 22, 2018, our stockholders approved amendments to the 2014 Plan and the 2014 Director Plan to increase the number of shares available for future grants under the Plans. 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 stock 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 compensation is recognized based on the number of awards to vest using actual forfeiture amounts. 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 income. For the three months ended March 31, 2018 and 2017 , stock compensation expense was $1.4 million and $2.0 million , respectively, and $2.9 million and $3.6 million for the six months ended March 31, 2018 and 2017 , respectively. Related income tax benefits recognized were $0.4 million and $0.7 million for the three months ended March 31, 2018 and 2017 , respectively, and $1.0 million and $1.4 million for the six months ended March 31, 2018 and 2017 , respectively. The following is a summary of the Plans’ restricted share and performance-based stock award activity as of March 31, 2018 and September 30, 2017 . The number of performance shares granted in the following table are reflected at the amount of achievement of the pre-established targets. March 31, 2018 September 30, 2017 Common Weighted-Average Grant Date Fair Value Common Weighted-Average Grant Date Fair Value Restricted Shares Restricted shares, beginning of fiscal year 180,337 $ 33.06 160,335 $ 26.89 Granted 89,003 41.07 90,363 39.35 Vested (81,999 ) 32.12 (68,293 ) 26.97 Forfeited (1,959 ) 40.30 (2,068 ) 30.91 Canceled — — — — Restricted shares, end of period 185,382 $ 37.25 180,337 $ 33.06 Vested, but not issuable at end of period 39,514 $ 32.90 29,287 $ 30.05 Performance Shares Performance shares, beginning of fiscal year 133,604 $ 33.39 236,185 $ 20.28 Granted 56,149 28.92 137,612 39.43 Vested — — (235,055 ) 18.00 Forfeited (2,178 ) 39.71 (5,138 ) 19.80 Canceled — — — — Performance shares, end of period $ 187,575 $ 35.63 $ 133,604 $ 33.39 Vested, but not issuable at end of period 5,612 $ 18.00 5,612 $ 18.00 As of March 31, 2018 , there was $7.8 million of unrecognized compensation cost related to nonvested restricted stock awards expected to be recognized over a period of 2.7 years . The fair value of the vested, but not issued stock awards at March 31, 2018 , was $1.8 million .

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements 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 mortgage-backed, states and political subdivisions, and other securities. Where Level 1 or Level 2 inputs are not available, securities are classified within Level 3 of the hierarchy. Level 3 securities were immaterial at March 31, 2018 and September 30, 2017 . Interest Rate Swaps and Loans Interest rate swaps are valued by the Company's Swap Dealers using cash flow valuation techniques with observable market data inputs. 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 the Company's Swap Dealers 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 has entered into Collateral Agreements with its Swap Dealers and Futures Clearing Merchant which entitle it to receive collateral to cover market values on derivatives which are in asset position, thus a credit risk adjustment on interest rate swaps is not warranted. The Company regularly 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, the fair values of which are calculated by applying observable market values from Fannie Mae TBA pricing to each interest rate lock commitment and forward sales contract, therefore, are classified within Level 2 of the valuation hierarchy. The Company also has back-to-back swaps with loan customers, with corresponding swaps with an outside third party in exact offsetting terms. 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, 2018 and September 30, 2017 . Fair Value Level 1 Level 2 Level 3 (dollars in thousands) As of March 31, 2018 U.S. Treasury securities $ 177,419 $ 177,419 $ — $ — Mortgage-backed securities 1,060,277 — 1,060,277 — States and political subdivision securities 68,900 — 67,935 965 Other 1,002 — 1,002 — Total securities available for sale $ 1,307,598 $ 177,419 $ 1,129,214 $ 965 Derivatives-assets $ 2,832 $ — $ 2,832 $ — Derivatives-liabilities 1,118 — 1,118 — Fair value loans 920,965 — 920,965 — Fair Value Level 1 Level 2 Level 3 (dollars in thousands) As of September 30, 2017 U.S. Treasury securities $ 228,603 $ 228,603 $ — $ — Mortgage-backed securities 1,065,737 — 1,065,737 — States and political subdivision securities 72,586 — 71,517 1,069 Other 1,034 — 1,034 — Total securities available for sale $ 1,367,960 $ 228,603 $ 1,138,288 $ 1,069 Derivatives-assets $ — $ — $ — $ — Derivatives-liabilities 17,155 — 17,155 — Fair value loans 1,016,576 — 1,016,576 — The following table presents the changes in Level 3 financial instruments for the three and six months ended March 31, 2018 and 2017 . Three Months Ended Six Months Ended March 31, 2018 March 31, 2017 March 31, 2018 March 31, 2017 (dollars in thousands) Balance, beginning of period $ 965 $ 1,224 $ 1,069 $ 1,315 Principal paydown — — (104 ) (91 ) Balance, end of period $ 965 $ 1,224 $ 965 $ 1,224 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. Other Repossessed Property Other repossessed property consists of loan collateral that has been repossessed through foreclosure. This collateral is comprised of commercial and residential real estate and other repossessed assets. Other repossessed property 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. 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. 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. Loan Servicing Rights Fair value is determined at a tranche level, based on market prices for comparable mortgage servicing contracts (Level 3), when available, or alternatively based on a valuation model that calculates the present value of estimated future net servicing income. The valuation model utilizes interest rate, prepayment speed, and default rate assumptions that market participants would use in estimating future net servicing income and that can be validated against market data (Level 3). Property Held for Sale This real estate property is carried in premises and equipment as property held for sale at fair value based upon the transactional price if available, or the appraised value of the property. 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, 2018 and September 30, 2017 . Fair Value Level 1 Level 2 Level 3 (dollars in thousands) As of March 31, 2018 Other repossessed property $ 7,679 $ — $ — $ 7,679 Impaired loans 198,609 — — 198,609 Loans held for sale, at lower of cost or fair value 2,429 — 2,429 — Loan servicing rights 3,586 — — 3,586 Property held for sale 1,109 — — 1,109 As of September 30, 2017 Other repossessed property $ 7,728 $ — $ — $ 7,728 Impaired loans 185,388 — — 185,388 Loans held for sale, at lower of cost or fair value 7,456 — 7,456 — Loan servicing rights 4,074 — — 4,074 Property held for sale 5,147 — — 5,147 The valuation techniques and significant unobservable inputs used to measure Level 3 fair value measurements at March 31, 2018 were as follows. Fair Value of Assets / (Liabilities) at March 31, 2018 Valuation Unobservable Range Weighted (dollars in thousands) Other repossessed property $ 7,679 Appraisal value Property specific adjustment N/A N/A Impaired loans 198,609 Appraisal value Property specific adjustment N/A N/A Loan servicing rights 3,586 Discounted cash flows Constant prepayment rate 7.9 - 20.5% 10.0 - 15.0% 10.4% 11.8% Property held for sale 1,109 Appraisal value Property specific adjustment N/A N/A Disclosures about 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 cash equivalents, 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, 2018 and September 30, 2017 are as follows. March 31, 2018 September 30, 2017 Level in Fair Value Hierarchy Carrying Amount Fair Carrying Amount Fair (dollars in thousands) Assets Cash and cash equivalents Level 1 $ 371,749 $ 371,749 $ 360,396 $ 360,396 Loans, net excluding fair valued loans and loans held for sale Level 3 8,349,772 8,238,751 7,881,018 7,798,134 Accrued interest receivable Level 2 49,353 49,353 53,176 53,176 Cash surrender value of life insurance policies Level 2 30,032 30,032 29,619 29,619 FHLB stock Level 2 33,720 33,720 37,551 37,551 Liabilities Deposits Level 2 $ 9,386,967 $ 9,384,577 $ 8,977,613 $ 8,978,926 FHLB advances and other borrowings Level 2 551,003 477,292 643,214 645,421 Securities sold under repurchase agreements Level 2 103,291 103,291 132,636 132,636 Accrued interest payable Level 2 6,165 6,165 4,405 4,405 Subordinated debentures and subordinated notes payable Level 2 108,385 107,826 108,302 108,293 The following methods and assumptions were used in estimating the fair value of financial instruments that were not previously disclosed. Cash and cash equivalents: 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. Cash Surrender Value of Life Insurance Policies: Fair value is equal to the cash surrender value of the life insurance policies and are categorized as Level 2 fair value measurement. FHLB stock: The carrying amount of FHLB stock approximates its fair value as it can only be redeemed with the FHLB at par value. FHLB 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 2 fair value measurement. FHLB advances and other borrowings: The fair value of FHLB advances 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 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 and Subordinated Notes Payable: The fair value of subordinated debentures and subordinated notes payable is estimated using discounted cash flow analysis, based on current incremental debt rates. Subordinated debentures and subordinated notes payable have been categorized as a Level 2 fair value measurement.

Earnings per Share

Earnings per Share	6 Months Ended
	Mar. 31, 2018
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. 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 and diluted earnings per share (EPS) for the three and six months ended March 31, 2018 and 2017 . Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands, except per share data) Net income $ 40,532 $ 35,162 $ 69,762 $ 72,065 Weighted average common shares outstanding 58,941,315 58,788,802 58,921,972 58,769,662 Dilutive effect of stock based compensation 204,802 284,867 194,951 263,125 Weighted average common shares outstanding for diluted earnings per share calculation 59,146,117 59,073,669 59,116,923 59,032,787 Basic earnings per share $ 0.69 $ 0.60 $ 1.18 $ 1.23 Diluted earnings per share $ 0.69 $ 0.60 $ 1.18 $ 1.22 The Company had 0 and 50,076 shares of unvested performance stock as of March 31, 2018 and 2017 , respectively, which were not included in the computation of diluted earnings per common share because performance conditions for vesting had not been met. The Company had 0 and 53,126 shares of anti-dilutive stock awards outstanding as of March 31, 2018 and 2017 , respectively.

Nature of Operations and Summ28

Nature of Operations and Summary of Significant Policies (Policies)	6 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation 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. Certain previously reported amounts have been reclassified to conform to the current presentation. The unaudited interim consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements for the year ended September 30, 2017 , 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 on the consolidated financial statements and accompanying notes. Actual results could differ from these estimates.
Subsequent Events	Subsequent Events The Company has evaluated all events or transactions that occurred through the date the Company issued these financial statements. Other than those events described below, there were no other material events that would require recognition in the consolidated financial statements or disclosure in the notes to the consolidated financial statements.
New Accounting Pronouncements	In February 2018, the Financial Accounting Standards Board ("FASB") issued ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allows for the reclassification of stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017 ("Tax Reform Act") from other comprehensive income to retained earnings. ASU 2018-02 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. The Company early adopted ASU 2018-02 during the second quarter of fiscal year 2018 with period of adoption application. Upon adoption, the Company made a policy election to reclassify stranded tax effects of approximately $2.4 million from accumulated other comprehensive income to retained earnings. In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities , which amends the hedge accounting recognition and presentation requirements in ASC 815 to improve the transparency and understandability of information conveyed to financial statement users about an entity’s risk management activities to better align the entity’s financial reporting for hedging relationships with those risk management activities and to reduce the complexity of and simplify the application of hedge accounting. ASU 2017-12 is to be applied to all existing hedging relationships on the date of adoption and will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted in any interim period, with the effect of adoption reflected as of the beginning of the fiscal year of adoption. The Company is currently evaluating the potential impact of ASU 2017-12 on our consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which addresses timelier recording of credit losses on loans and other financial instruments held by financial institutions and other organizations. ASU 2016-13 requires institutions to measure all expected credit losses related to financial assets measured at amortized costs with an expected loss model based on historical experience, current conditions and reasonable and supportable forecasts relevant to affect the collectability of the financial assets, which is referred to as the current expected credit loss (CECL) model. ASU 2016-13 requires enhanced disclosures, including qualitative and quantitative requirements, to help understand significant estimates and judgments used in estimating credit losses, as well as provide additional information about the amounts recorded in the financial statements. ASU 2016-13 will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019, with early adoption permitted after December 15, 2018. The amendment requires the use of the modified retrospective approach for adoption. The Company has formed a project team to work on the implementation of ASU 2016-13 and is currently evaluating the potential impact on our consolidated financial statements. In February 2016, the FASB issued ASU 2016-02 , Leases (Topic 842) , which requires that lessees recognize the assets and liabilities arising from leases on the balance sheet and disclosing key information about leasing arrangements. Lessees will be required to recognize an obligation for future lease payments measured on a discounted basis and a related right-of-use asset. ASU 2016-02 does not significantly change lease accounting requirements applicable to lessors; however, certain changes were made to align, where necessary, lessor accounting with the lessee accounting model and ASC Topic 606, "Revenue from Contracts with Customers." ASU 2016-02 will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. The Company is currently evaluating the potential impact of ASU 2016-02 on our consolidated financial statements. In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10) - Recognition and Measurement of Financial Assets and Financial Liabilities , which requires equity investments, in general, to be measured at fair value with changes in fair value recognized in earnings. It also eliminates the requirement to disclose the methods and significant assumptions used to estimate the fair value for financial instruments measured at amortized cost, requires entities to use the exit price notion when measuring fair value, requires an entity to present separately in other comprehensive income the portion of the total change in fair value of a liability resulting from a change in the measurement category and form on the balance sheet or accompanying notes, clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available for sale securities in combination with the entity's other deferred tax assets, and simplifies the impairment assessment of equity investments without readily determinable fair values. ASU 2016-01 will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017, with early adoption permitted. The Company does not believe ASU 2016-01 will have a material impact on our consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which implements a more robust framework that clarifies the principles for recognizing revenue and gives greater consistency and comparability in revenue recognition practices. In the new framework, an entity recognizes revenue in an amount that reflects the consideration to which the entity expects to be entitled in exchange for goods or services. The new model requires the identification of performance obligations included in the contract with customers, a determination of the transaction price and an allocation of the price to those performance obligations. The entity recognizes revenue when performance obligations are satisfied. In August 2015, the FASB issued ASU 2015-14, which deferred the effective date of ASU 2014-09 to annual reporting periods beginning after December 15, 2017. In March 2016, the FASB issued ASU 2016-08, which intends to improve the operability and understandability of the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, which clarifies guidance pertaining to the identification of performance obligations and the licensing implementation. In May 2016, the FASB issued ASU 2016-11 and 2016-12, which further clarify guidance and provide practical expedients related to the adoption of ASU 2014-09. The standard permits the use of either the retrospective or cumulative effect transition method. The standard, along with subsequent guidance from FASB, lists several items that are specifically out of scope for ASU 2014-09, including but not limited to core interest income, derivative instruments, investments, and loan origination fees. To address the new standard, the Company formed a working group and has completed the initial scoping phase to determine which revenue streams may be subject to accounting or disclosure changes upon adoption in October of 2018. Subsequent to this initial scoping, the Company selected a representative sample of contracts from the in-scope revenue streams for review under the amended guidance ("key contracts"). The review of key contracts is in process. Based on this preliminary analysis, we do not anticipate significant changes as a result of implementing the standard, but will conclude on the quantitative and qualitative impacts once we have completed our review of key contracts for any in-scope items over the coming months.

Nature of Operations and Summ29

Nature of Operations and Summary of Significant Policies (Tables)	6 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Schedule of correction of prior period balances	As a result, the consolidated statements of income have been revised to reflect these changes as follows. As originally reported Adjustments As revised (dollars in thousands) Three months ended March 31, 2017 Interest income - loans $ 101,136 $ (1,655 ) $ 99,481 Noninterest income - service charges and other fees 11,919 1,655 13,574 Six months ended March 31, 2017 Interest income - loans $ 202,818 $ (3,405 ) $ 199,413 Noninterest income - service charges and other fees 24,005 3,405 27,410 As originally reported Adjustments As revised (dollars in thousands) Twelve months ended September 30, 2017 Interest income - loans $ 414,434 $ (7,152 ) $ 407,282 Noninterest income - service charges and other fees 48,573 7,152 55,725 Twelve months ended September 30, 2016 Interest income - loans $ 370,444 $ (6,716 ) $ 363,728 Noninterest income - service charges and other fees 46,209 6,716 52,925

Securities Available for Sale (

Securities Available for Sale (Tables)	6 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of amortized cost and fair value of investments	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. Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated (dollars in thousands) As of March 31, 2018 U.S. Treasury securities $ 178,563 $ — $ (1,144 ) $ 177,419 Mortgage-backed securities: Government National Mortgage Association 452,297 47 (13,971 ) 438,373 Federal Home Loan Mortgage Corporation 218,838 3 (4,878 ) 213,963 Federal National Mortgage Association 179,268 — (4,591 ) 174,677 Small Business Assistance Program 237,156 144 (4,036 ) 233,264 States and political subdivision securities 70,513 10 (1,623 ) 68,900 Other 1,006 — (4 ) 1,002 Total $ 1,337,641 $ 204 $ (30,247 ) $ 1,307,598 Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated (dollars in thousands) As of September 30, 2017 U.S. Treasury securities $ 228,039 $ 579 $ (15 ) $ 228,603 Mortgage-backed securities: Government National Mortgage Association 511,457 228 (6,635 ) 505,050 Federal Home Loan Mortgage Corporation 169,147 75 (1,247 ) 167,975 Federal National Mortgage Association 170,247 22 (1,287 ) 168,982 Small Business Assistance Program 224,005 726 (1,001 ) 223,730 States and political subdivision securities 73,041 187 (642 ) 72,586 Other 1,006 28 — 1,034 Total $ 1,376,942 $ 1,845 $ (10,827 ) $ 1,367,960
Schedule of amortized cost and fair value of investments by contractual maturity	The amortized cost and approximate fair value of debt securities available for sale as of March 31, 2018 and September 30, 2017 , 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 penalty. March 31, 2018 September 30, 2017 Amortized Estimated Amortized Estimated (dollars in thousands) Due in one year or less $ 43,291 $ 43,204 $ 91,535 $ 91,597 Due after one year through five years 189,787 187,741 193,117 193,373 Due after five years through ten years 15,876 15,252 16,306 16,097 Due after ten years 122 122 122 122 249,076 246,319 301,080 301,189 Mortgage-backed securities 1,087,559 1,060,277 1,074,856 1,065,737 Securities without contractual maturities 1,006 1,002 1,006 1,034 Total $ 1,337,641 $ 1,307,598 $ 1,376,942 $ 1,367,960
Schedule of gross unrealized losses 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. Less than 12 months 12 months or more Total Estimated Unrealized Estimated Unrealized Estimated Unrealized (dollars in thousands) As of March 31, 2018 U.S. Treasury securities $ 148,360 $ (873 ) $ 29,059 $ (271 ) $ 177,419 $ (1,144 ) Mortgage-backed securities 314,049 (4,765 ) 712,510 (22,711 ) 1,026,559 (27,476 ) States and political subdivision securities 14,967 (109 ) 49,249 (1,514 ) 64,216 (1,623 ) Other 1,002 (4 ) — — 1,002 (4 ) Total $ 478,378 $ (5,751 ) $ 790,818 $ (24,496 ) $ 1,269,196 $ (30,247 ) Less than 12 months 12 months or more Total Estimated Unrealized Estimated Unrealized Estimated Unrealized (dollars in thousands) As of September 30, 2017 U.S. Treasury securities $ 10,003 $ (15 ) $ — $ — $ 10,003 $ (15 ) Mortgage-backed securities 635,969 (5,425 ) 241,368 (4,746 ) 877,337 (10,171 ) States and political subdivision securities 21,705 (197 ) 25,773 (444 ) 47,478 (641 ) Other — — — — — — Total $ 667,677 $ (5,637 ) $ 267,141 $ (5,190 ) $ 934,818 $ (10,827 )

Loans (Tables)

Loans (Tables)	6 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Schedule of loans receivable	The composition of loans as of March 31, 2018 and September 30, 2017 , is as follows. March 31, 2018 September 30, 2017 (dollars in thousands) Commercial real estate $ 4,467,778 $ 4,124,805 Agriculture 2,177,020 2,122,138 Commercial non-real estate 1,767,587 1,718,914 Residential real estate 866,982 932,892 Consumer 55,190 66,559 Other 41,816 43,207 Ending balance 9,376,373 9,008,515 Less: Unamortized discount on acquired loans (23,501 ) (29,121 ) Unearned net deferred fees and costs and loans in process (14,566 ) (10,841 ) Total $ 9,338,306 $ 8,968,553
Schedule of the Company's nonaccrual loans	The following table presents the Company’s nonaccrual loans at March 31, 2018 and September 30, 2017 , excluding ASC 310-30 loans. Loans greater than 90 days past due and still accruing interest as of March 31, 2018 and September 30, 2017 , were $0.9 million and $1.9 million , respectively. March 31, 2018 September 30, 2017 (dollars in thousands) Nonaccrual loans Commercial real estate $ 26,343 $ 14,693 Agriculture 86,758 99,325 Commercial non-real estate 10,146 13,674 Residential real estate 4,058 4,421 Consumer 88 112 Total $ 127,393 $ 132,225
Schedule of the composition of the loan portfolio by internal risk rating	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 $921.0 million at March 31, 2018 and $1.02 billion at September 30, 2017 . As of March 31, 2018 Commercial Real Estate Agriculture Commercial Residential Real Estate Consumer Other Total (dollars in thousands) Credit Risk Profile by Internally Assigned Grade Grade: Pass $ 3,888,128 $ 1,683,280 $ 1,443,731 $ 798,778 $ 54,324 $ 41,816 $ 7,910,057 Watchlist 62,695 152,878 33,852 4,935 326 — 254,686 Substandard 62,784 123,714 19,552 7,152 235 — 213,437 Doubtful 113 5 2,756 126 — — 3,000 Loss — — — — — — — Ending balance 4,013,720 1,959,877 1,499,891 810,991 54,885 41,816 8,381,180 Loans covered by a FDIC loss sharing agreement — — — 50,727 — — 50,727 Total $ 4,013,720 $ 1,959,877 $ 1,499,891 $ 861,718 $ 54,885 $ 41,816 $ 8,431,907 As of September 30, 2017 Commercial Real Estate Agriculture Commercial Residential Real Estate Consumer Other Total (dollars in thousands) Credit Risk Profile by Internally Assigned Grade Grade: Pass $ 3,519,689 $ 1,577,403 $ 1,369,803 $ 853,266 $ 65,673 $ 43,207 $ 7,429,041 Watchlist 80,195 157,407 31,878 4,158 187 — 273,825 Substandard 37,627 130,953 21,438 7,368 306 — 197,692 Doubtful 521 119 3,841 242 — — 4,723 Loss — — — — — — — Ending balance 3,638,032 1,865,882 1,426,960 865,034 66,166 43,207 7,905,281 Loans covered by a FDIC loss sharing agreement — — — 57,537 — — 57,537 Total $ 3,638,032 $ 1,865,882 $ 1,426,960 $ 922,571 $ 66,166 $ 43,207 $ 7,962,818
Schedule of past due loans	The following table presents the Company’s past due loans at March 31, 2018 and September 30, 2017 . 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 $921.0 million at March 31, 2018 and $1.02 billion at September 30, 2017 . 30-59 Days Past Due 60-89 Days Past Due 90 Days or Greater Past Due Total Current Total Financing Receivables (dollars in thousands) As of March 31, 2018 Commercial real estate $ 3,308 $ 67 $ 22,319 $ 25,694 $ 3,988,026 $ 4,013,720 Agriculture 2,387 371 26,498 29,256 1,930,621 1,959,877 Commercial non-real estate 3,665 1,190 5,223 10,078 1,489,813 1,499,891 Residential real estate 2,568 90 1,364 4,022 806,969 810,991 Consumer 140 3 44 187 54,698 54,885 Other — — — — 41,816 41,816 Ending balance 12,068 1,721 55,448 69,237 8,311,943 8,381,180 Loans covered by a FDIC loss sharing agreement 1,283 217 588 2,088 48,639 50,727 Total $ 13,351 $ 1,938 $ 56,036 $ 71,325 $ 8,360,582 $ 8,431,907 30-59 Days Past Due 60-89 Days Past Due 90 Days or Greater Past Due Total Current Total Financing Receivables (dollars in thousands) As of September 30, 2017 Commercial real estate $ 876 $ 22,536 $ 6,504 $ 29,916 $ 3,608,116 $ 3,638,032 Agriculture 1,453 3,181 20,844 25,478 1,840,404 1,865,882 Commercial non-real estate 2,485 115 8,580 11,180 1,415,780 1,426,960 Residential real estate 1,428 76 951 2,455 862,579 865,034 Consumer 71 24 18 113 66,053 66,166 Other — — — — 43,207 43,207 Ending balance 6,313 25,932 36,897 69,142 7,836,139 7,905,281 Loans covered by a FDIC loss sharing agreement 998 54 738 1,790 55,747 57,537 Total $ 7,311 $ 25,986 $ 37,635 $ 70,932 $ 7,891,886 $ 7,962,818
Schedule of impaired loans	The following table presents the Company’s impaired loans. This table excludes purchased credit impaired loans and loans measured at fair value with changes in fair value reported in earnings of $921.0 million at March 31, 2018 and $1.02 billion at September 30, 2017 . March 31, 2018 September 30, 2017 Recorded Investment Unpaid Principal Balance Related Allowance Recorded Investment Unpaid Principal Balance Related Allowance (dollars in thousands) Impaired loans: With an allowance recorded: Commercial real estate $ 48,532 $ 49,799 $ 7,248 $ 20,819 $ 24,893 $ 3,621 Agriculture 63,293 73,823 10,465 79,219 88,268 11,468 Commercial non-real estate 14,747 18,140 4,320 17,950 28,755 4,779 Residential real estate 5,208 5,991 2,549 5,177 5,874 2,581 Consumer 217 225 74 280 287 86 Total impaired loans with an allowance recorded 131,997 147,978 24,656 123,445 148,077 22,535 With no allowance recorded: Commercial real estate 13,335 52,866 — 16,652 69,677 — Agriculture 61,643 66,567 — 51,256 64,177 — Commercial non-real estate 14,110 23,372 — 13,983 38,924 — Residential real estate 2,166 5,157 — 2,574 9,613 — Consumer 14 133 — 13 950 — Total impaired loans with no allowance recorded 91,268 148,095 — 84,478 183,341 — Total impaired loans $ 223,265 $ 296,073 $ 24,656 $ 207,923 $ 331,418 $ 22,535 The following table presents the average recorded investment on impaired loans and interest income recognized on impaired loans for the three and six months ended March 31, 2018 and 2017 , respectively, are as follows. Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Average Recorded Investment Interest Income Recognized While on Impaired Status Average Recorded Investment Interest Income Recognized While on Impaired Status Average Recorded Investment Interest Income Recognized While on Impaired Status Average Recorded Investment Interest Income Recognized While on Impaired Status (dollars in thousands) Commercial real estate $ 66,577 $ 477 $ 44,807 $ 545 $ 56,875 $ 2,053 $ 47,873 $ 1,215 Agriculture 121,062 1,189 128,919 1,326 124,200 2,171 119,892 3,193 Commercial non-real estate 30,350 325 46,304 358 30,878 776 47,477 780 Residential real estate 7,578 116 9,565 126 7,636 281 9,831 240 Consumer 238 4 389 12 256 8 391 27 Total $ 225,805 $ 2,111 $ 229,984 $ 2,367 $ 219,845 $ 5,289 $ 225,464 $ 5,455 The following table provides purchased credit impaired loans at March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 Outstanding Balance ¹ Recorded Investment ² Carrying Value ³ Outstanding Balance ¹ Recorded Investment ² Carrying Value ³ (dollars in thousands) Commercial real estate $ 105,489 $ 28,494 $ 27,778 $ 110,797 $ 30,099 $ 29,417 Agriculture 5,813 2,746 2,746 10,463 7,174 7,059 Commercial non-real estate 10,001 2,231 2,231 9,825 1,920 1,920 Residential real estate 55,326 46,945 46,827 61,981 52,736 52,540 Consumer 668 534 534 798 666 666 Total lending $ 177,297 $ 80,950 $ 80,116 $ 193,864 $ 92,595 $ 91,602 1 Represents the legal balance of ASC 310-30 loans. 2 Represents the book balance of ASC 310-30 loans. 3 Represents the book balance of ASC 310-30 loans net of the related allowance for loan and lease losses.
Summary of troubled debt restructurings on accruing and nonaccrual loans	The following table presents the recorded value of the Company’s TDR balances as of March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 Accruing Nonaccrual Accruing Nonaccrual (dollars in thousands) Commercial real estate $ 617 $ 2,632 $ 1,121 $ 5,351 Agriculture 29,200 60,098 22,678 59,633 Commercial non real estate 7,647 3,916 8,369 5,641 Real estate 249 739 311 688 Consumer 83 — 11 21 Total $ 37,796 $ 67,385 $ 32,490 $ 71,334 The following table presents a summary of all accruing loans restructured in TDRs during the three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Recorded Investment Recorded Investment Number Pre-Modification Post-Modification Number Pre-Modification Post-Modification (dollars in thousands) Commercial real estate Rate modification — $ — $ — — $ — $ — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial real estate — — — — — — Agriculture Rate modification 1 5,500 5,500 — — — Term extension — — — 2 8,434 8,434 Payment modification 1 573 573 — — — Bankruptcy — — — — — — Other — — — — — — Total agriculture 2 6,073 6,073 2 8,434 8,434 Commercial non-real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — 2 93 93 Bankruptcy — — — — — — Other — — — — — — Total commercial non-real estate — — — 2 93 93 Residential real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total residential real estate — — — — — — Consumer Rate modification 1 73 73 — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total consumer 1 73 73 — — — Total accruing 3 $ 6,146 $ 6,146 4 $ 8,527 $ 8,527 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 accruing loans restructured in TDRs during the six months ended March 31, 2018 and 2017 . Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Recorded Investment Recorded Investment Number Pre-Modification Post-Modification Number Pre-Modification Post-Modification (dollars in thousands) Commercial real estate Rate modification — $ — $ — — $ — $ — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial real estate — — — — — — Agriculture Rate modification 1 5,500 5,500 — — — Term extension — — — 2 8,434 8,434 Payment modification 1 573 573 — — — Bankruptcy — — — — — — Other — — — — — — Total agriculture 2 6,073 6,073 2 8,434 8,434 Commercial non-real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — 4 526 526 Bankruptcy — — — — — — Other — — — — — — Total commercial non-real estate — — — 4 526 526 Residential real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — 1 9 9 Bankruptcy — — — — — — Other — — — — — — Total residential real estate — — — 1 9 9 Consumer Rate modification 1 73 73 — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total consumer 1 73 73 — — — Total accruing 3 $ 6,146 $ 6,146 7 $ 8,969 $ 8,969 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 three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Recorded Investment Recorded Investment Number Pre-Modification Post-Modification Number Pre-Modification Post-Modification (dollars in thousands) Commercial real estate Rate modification — $ — $ — — $ — $ — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial real estate — — — — — — Agriculture Rate modification — — — — — — Term extension 3 6,324 6,324 6 12,988 12,988 Payment modification 3 2,050 2,050 — — — Bankruptcy — — — — — — Other — — — — — — Total agriculture 6 8,374 8,374 6 12,988 12,988 Commercial non-real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial non-real estate — — — — — — Residential real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total residential real estate — — — — — — Consumer Rate modification — — — — — — Term extension — — — 3 21 21 Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total consumer — — — 3 21 21 Total non-accruing 6 $ 8,374 $ 8,374 9 $ 13,009 $ 13,009 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, 2018 and 2017 . Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Recorded Investment Recorded Investment Number Pre-Modification Post-Modification Number Pre-Modification Post-Modification (dollars in thousands) Commercial real estate Rate modification — $ — $ — — $ — $ — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial real estate — — — — — — Agriculture Rate modification — — — — — — Term extension 3 6,324 6,324 6 12,988 12,988 Payment modification 3 2,050 2,050 — — — Bankruptcy — — — — — — Other — — — — — — Total agriculture 6 8,374 8,374 6 12,988 12,988 Commercial non-real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total commercial non-real estate — — — — — — Residential real estate Rate modification — — — — — — Term extension — — — — — — Payment modification — — — 1 21 21 Bankruptcy — — — — — — Other — — — — — — Total residential real estate — — — 1 21 21 Consumer Rate modification — — — — — — Term extension — — — 3 21 21 Payment modification — — — — — — Bankruptcy — — — — — — Other — — — — — — Total consumer — — — 3 21 21 Total non-accruing 6 $ 8,374 $ 8,374 10 $ 13,030 $ 13,030 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 loans that were modified as TDRs within the previous 12 months and for which there was a payment default for the three and six months ended March 31, 2018 and 2017 , respectively. Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment (dollars in thousands) Commercial real estate — $ — — $ — 1 $ 1,012 1 $ 34 Agriculture 3 4,264 — — 4 5,011 — — Commercial non-real estate — — 1 — — — 1 — Residential real estate — — — — — — — — Consumer — — — — — — — — Total 3 $ 4,264 1 $ — 5 $ 6,023 2 $ 34

Allowance for Loan and Lease 32

Allowance for Loan and Lease Losses (Tables)	6 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Summary of allowances for loan and lease losses	The following tables present the Company’s allowance for loan and lease losses roll forward for the three and six months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Beginning balance January 1, 2018 $ 15,995 $ 24,750 $ 16,434 $ 5,475 $ 307 $ 1,062 $ 64,023 Charge-offs (1,268 ) (783 ) (1,605 ) (20 ) (62 ) (557 ) (4,295 ) Recoveries 61 125 88 27 20 190 511 Provision 4,077 152 813 (341 ) 14 281 4,996 Impairment (improvement) of ASC 310-30 loans 49 (115 ) — (30 ) — — (96 ) Ending balance March 31, 2018 $ 18,914 $ 24,129 $ 15,730 $ 5,111 $ 279 $ 976 $ 65,139 Three Months Ended March 31, 2017 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Beginning balance January 1, 2017 $ 16,623 $ 28,519 $ 13,443 $ 6,786 $ 340 $ 1,056 $ 66,767 Charge-offs (1,824 ) (4,554 ) (1,734 ) (117 ) (31 ) (819 ) (9,079 ) Recoveries 286 118 121 56 15 392 988 Provision 2,096 2,237 119 210 47 351 5,060 (Improvement) of ASC 310-30 loans (185 ) — — (866 ) — — (1,051 ) Ending balance March 31, 2017 $ 16,996 $ 26,320 $ 11,949 $ 6,069 $ 371 $ 980 $ 62,685 Six Months Ended March 31, 2018 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Beginning balance October 1, 2017 $ 16,941 $ 25,757 $ 14,114 $ 5,347 $ 329 $ 1,015 $ 63,503 Charge-offs (1,597 ) (2,981 ) (2,844 ) (275 ) (116 ) (1,091 ) (8,904 ) Recoveries 209 172 209 117 42 334 1,083 Provision 3,322 1,296 4,251 (11 ) 24 718 9,600 Impairment (improvement) of ASC 310-30 loans 39 (115 ) — (67 ) — — (143 ) Ending balance March 31, 2018 $ 18,914 $ 24,129 $ 15,730 $ 5,111 $ 279 $ 976 $ 65,139 Six Months Ended March 31, 2017 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Beginning balance October 1, 2016 $ 17,946 $ 25,115 $ 12,990 $ 7,106 $ 438 $ 1,047 $ 64,642 Charge-offs (1,824 ) (7,420 ) (3,693 ) (267 ) (110 ) (1,317 ) (14,631 ) Recoveries 385 144 219 262 30 576 1,616 Provision 549 8,481 2,433 (140 ) 13 674 12,010 (Improvement) of ASC 310-30 loans (60 ) — — (892 ) — — (952 ) Ending balance March 31, 2017 $ 16,996 $ 26,320 $ 11,949 $ 6,069 $ 371 $ 980 $ 62,685 The following tables provide details regarding the allowance for loan and lease losses and balance by type of allowance as of March 31, 2018 and September 30, 2017 . These tables are presented net of unamortized discount on acquired loans and excludes loans of $921.0 million measured at fair value, loans held for sale of $2.4 million , and guaranteed loans of $161.5 million for March 31, 2018 and loans measured at fair value of $1.02 billion , loans held for sale of $7.5 million , and guaranteed loans of $168.3 million for September 30, 2017 . As of March 31, 2018 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Allowance for loan and lease losses Individually evaluated for impairment $ 7,248 $ 10,465 $ 4,320 $ 2,549 $ 74 $ — $ 24,656 Collectively evaluated for impairment 10,950 13,664 11,410 2,444 205 976 39,649 ASC 310-30 loans 716 — — 118 — — 834 Total allowance $ 18,914 $ 24,129 $ 15,730 $ 5,111 $ 279 $ 976 $ 65,139 Financing Receivables Individually evaluated for impairment $ 61,867 $ 124,936 $ 28,857 $ 7,374 $ 231 $ — $ 223,265 Collectively evaluated for impairment 3,846,737 1,808,883 1,407,897 804,298 54,120 41,816 7,963,751 ASC 310-30 loans 28,494 2,746 2,231 46,945 534 — 80,950 Loans Outstanding $ 3,937,098 $ 1,936,565 $ 1,438,985 $ 858,617 $ 54,885 $ 41,816 $ 8,267,966 As of September 30, 2017 Commercial Real Estate Agriculture Commercial Non-Real Estate Residential Real Estate Consumer Other Total (dollars in thousands) Allowance for loan and lease losses Individually evaluated for impairment $ 3,621 $ 11,468 $ 4,779 $ 2,581 $ 86 $ — $ 22,535 Collectively evaluated for impairment 12,638 14,174 9,335 2,570 243 1,015 39,975 ASC 310-30 loans 682 115 — 196 — — 993 Total allowance $ 16,941 $ 25,757 $ 14,114 $ 5,347 $ 329 $ 1,015 $ 63,503 Financing Receivables Individually evaluated for impairment $ 37,471 $ 130,475 $ 31,933 $ 7,751 $ 293 $ — $ 207,923 Collectively evaluated for impairment 3,487,232 1,702,634 1,333,888 854,330 65,207 43,207 7,486,498 ASC 310-30 loans 30,099 7,174 1,920 52,736 666 — 92,595 Loans Outstanding $ 3,554,802 $ 1,840,283 $ 1,367,741 $ 914,817 $ 66,166 $ 43,207 $ 7,787,016

Accounting for Certain Loans 33

Accounting for Certain Loans Acquired with Deteriorated Credit Quality (Tables)	6 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Schedule of troubled debt restructurings	The re-assessment of purchased credit impaired loans resulted in the following changes in the accretable yield during the three and six months ended March 31, 2018 and 2017 . Three Months Ended Six Months Ended March 31, 2018 March 31, 2017 March 31, 2018 March 31, 2017 (dollars in thousands) Balance at beginning of period $ 41,918 $ 39,758 $ 44,131 $ 38,124 Accretion (3,664 ) (3,040 ) (7,045 ) (5,978 ) Reclassification from nonaccretable difference (413 ) 1,987 755 6,559 Balance at end of period $ 37,841 $ 38,705 $ 37,841 $ 38,705
Schedule of impaired loans	The following table presents the Company’s impaired loans. This table excludes purchased credit impaired loans and loans measured at fair value with changes in fair value reported in earnings of $921.0 million at March 31, 2018 and $1.02 billion at September 30, 2017 . March 31, 2018 September 30, 2017 Recorded Investment Unpaid Principal Balance Related Allowance Recorded Investment Unpaid Principal Balance Related Allowance (dollars in thousands) Impaired loans: With an allowance recorded: Commercial real estate $ 48,532 $ 49,799 $ 7,248 $ 20,819 $ 24,893 $ 3,621 Agriculture 63,293 73,823 10,465 79,219 88,268 11,468 Commercial non-real estate 14,747 18,140 4,320 17,950 28,755 4,779 Residential real estate 5,208 5,991 2,549 5,177 5,874 2,581 Consumer 217 225 74 280 287 86 Total impaired loans with an allowance recorded 131,997 147,978 24,656 123,445 148,077 22,535 With no allowance recorded: Commercial real estate 13,335 52,866 — 16,652 69,677 — Agriculture 61,643 66,567 — 51,256 64,177 — Commercial non-real estate 14,110 23,372 — 13,983 38,924 — Residential real estate 2,166 5,157 — 2,574 9,613 — Consumer 14 133 — 13 950 — Total impaired loans with no allowance recorded 91,268 148,095 — 84,478 183,341 — Total impaired loans $ 223,265 $ 296,073 $ 24,656 $ 207,923 $ 331,418 $ 22,535 The following table presents the average recorded investment on impaired loans and interest income recognized on impaired loans for the three and six months ended March 31, 2018 and 2017 , respectively, are as follows. Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Average Recorded Investment Interest Income Recognized While on Impaired Status Average Recorded Investment Interest Income Recognized While on Impaired Status Average Recorded Investment Interest Income Recognized While on Impaired Status Average Recorded Investment Interest Income Recognized While on Impaired Status (dollars in thousands) Commercial real estate $ 66,577 $ 477 $ 44,807 $ 545 $ 56,875 $ 2,053 $ 47,873 $ 1,215 Agriculture 121,062 1,189 128,919 1,326 124,200 2,171 119,892 3,193 Commercial non-real estate 30,350 325 46,304 358 30,878 776 47,477 780 Residential real estate 7,578 116 9,565 126 7,636 281 9,831 240 Consumer 238 4 389 12 256 8 391 27 Total $ 225,805 $ 2,111 $ 229,984 $ 2,367 $ 219,845 $ 5,289 $ 225,464 $ 5,455 The following table provides purchased credit impaired loans at March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 Outstanding Balance ¹ Recorded Investment ² Carrying Value ³ Outstanding Balance ¹ Recorded Investment ² Carrying Value ³ (dollars in thousands) Commercial real estate $ 105,489 $ 28,494 $ 27,778 $ 110,797 $ 30,099 $ 29,417 Agriculture 5,813 2,746 2,746 10,463 7,174 7,059 Commercial non-real estate 10,001 2,231 2,231 9,825 1,920 1,920 Residential real estate 55,326 46,945 46,827 61,981 52,736 52,540 Consumer 668 534 534 798 666 666 Total lending $ 177,297 $ 80,950 $ 80,116 $ 193,864 $ 92,595 $ 91,602 1 Represents the legal balance of ASC 310-30 loans. 2 Represents the book balance of ASC 310-30 loans. 3 Represents the book balance of ASC 310-30 loans net of the related allowance for loan and lease losses.

FDIC Indemnification Asset (Tab

FDIC Indemnification Asset (Tables)	6 Months Ended
	Mar. 31, 2018
Banking and Thrift [Abstract]
Summary of FDIC indemnification asset activity	The following table represents a summary of the activity related to the FDIC indemnification asset for the three and six months ended March 31, 2018 and 2017 . Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands) Balance at beginning of period $ 4,692 $ 9,887 $ 5,704 $ 10,777 Amortization (671 ) (1,114 ) (1,689 ) (1,981 ) Changes in expected reimbursements from FDIC for changes in expected credit losses (76 ) (133 ) (94 ) (105 ) Changes in reimbursable expenses (456 ) (299 ) (662 ) (538 ) Reimbursements of covered losses to the FDIC 189 30 419 218 Balance at end of period $ 3,678 $ 8,371 $ 3,678 $ 8,371

Derivative Financial Instrume35

Derivative Financial Instruments (Tables)	6 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of derivative positions, notional amounts and estimated fair values	The following table presents the notional amounts and gross fair values of all derivative assets and liabilities held by the Company as of March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 Notional Amount Gross Gross Notional Amount Gross Gross (dollars in thousands) Derivatives not designated as hedging instruments: Interest rate swaps Financial institution counterparties $ 1,039,100 $ 17,185 $ (6,943 ) $ 1,025,474 $ 4,967 $ (22,737 ) Customer counterparties 118,606 1,602 (1,112 ) 36,072 615 — Mortgage loan commitments 27,499 3 — 37,765 — (48 ) Mortgage loan forward sale contracts 27,398 — (3 ) 43,628 48 — Total $ 1,212,603 $ 18,790 $ (8,058 ) $ 1,142,939 $ 5,630 $ (22,785 )
Summary of offsetting assets	The following tables provide information on the Company's netting adjustments as of March 31, 2018 and September 30, 2017 . Amounts offset on the Consolidated Balance Sheet Gross Fair Value Fair Value Offset Amount Cash Collateral Net Amount Presented on the Consolidated Balance Sheet (dollars in thousands) March 31, 2018 Total Derivative Assets $ 18,790 $ (6,943 ) $ (9,015 ) $ 2,832 Total Derivative Liabilities ¹ $ (8,058 ) $ 6,943 $ (3 ) $ (1,118 ) 1 In addition to the cash collateral, there were securities of $5.0 million posted as collateral for financial institution counterparties at March 31, 2018. Amounts offset on the Consolidated Balance Sheet Gross Fair Value Fair Value Offset Amount Cash Collateral Net Amount Presented on the Consolidated Balance Sheet (dollars in thousands) September 30, 2017 Total Derivative Assets $ 1,850 $ (1,850 ) $ — $ — Total Derivative Liabilities ¹ ² (19,005 ) 1,850 — (17,155 ) 1 In addition to the cash collateral, there were securities of $25.0 million posted as collateral for financial institution counterparties at September 30, 2017. 2 There was an additional $2.3 million of collateral held for initial margin with our Futures Clearing Merchant for clearing derivatives at September 30, 2017 and is included in other assets in the consolidated balance sheets.
Summary of offsetting liabilities	The following tables provide information on the Company's netting adjustments as of March 31, 2018 and September 30, 2017 . Amounts offset on the Consolidated Balance Sheet Gross Fair Value Fair Value Offset Amount Cash Collateral Net Amount Presented on the Consolidated Balance Sheet (dollars in thousands) March 31, 2018 Total Derivative Assets $ 18,790 $ (6,943 ) $ (9,015 ) $ 2,832 Total Derivative Liabilities ¹ $ (8,058 ) $ 6,943 $ (3 ) $ (1,118 ) 1 In addition to the cash collateral, there were securities of $5.0 million posted as collateral for financial institution counterparties at March 31, 2018. Amounts offset on the Consolidated Balance Sheet Gross Fair Value Fair Value Offset Amount Cash Collateral Net Amount Presented on the Consolidated Balance Sheet (dollars in thousands) September 30, 2017 Total Derivative Assets $ 1,850 $ (1,850 ) $ — $ — Total Derivative Liabilities ¹ ² (19,005 ) 1,850 — (17,155 ) 1 In addition to the cash collateral, there were securities of $25.0 million posted as collateral for financial institution counterparties at September 30, 2017. 2 There was an additional $2.3 million of collateral held for initial margin with our Futures Clearing Merchant for clearing derivatives at September 30, 2017 and is included in other assets in the consolidated balance sheets.
Schedule of derivative instruments, effect on other comprehensive income	The effect of derivatives on the consolidated statements of income for the three and six months ended March 31, 2018 and 2017 was as follows. Amount of Gain (Loss) Recognized in Statements of Income Three Months Ended Six Months Ended Location of Gain (Loss) Recognized in Statements of Income March 31, 2018 March 31, 2017 March 31, 2018 March 31, 2017 (dollars in thousands) Derivatives not designated as hedging instruments: Interest rate swaps Net realized and unrealized gain on derivatives $ 14,282 $ 1,592 $ 21,509 $ 60,568 Mortgage loan commitments Net realized and unrealized gain on derivatives 2 158 3 53 Mortgage loan forward sale contracts Net realized and unrealized gain on derivatives (2 ) (158 ) (3 ) (53 )

The Fair Value Option for Cer36

The Fair Value Option for Certain Loans (Tables)	6 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Summary of the 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 within the consolidated statements of income are as follows for the three and six months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Six Months Ended March 31, 2018 Six Months Ended March 31, 2017 Noninterest Income Total Changes in Fair Value Noninterest Income Total Changes in Fair Value Noninterest Income Total Changes in Fair Value Noninterest Income Total Changes in Fair Value (dollars in thousands) Long-term loans $ (14,838 ) $ (14,838 ) $ (5,216 ) $ (5,216 ) $ (23,502 ) $ (23,502 ) $ (69,218 ) $ (69,218 )

Core Deposits and Other Intan37

Core Deposits and Other Intangibles (Tables)	6 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of finite-lived intangible assets	The following table presents a summary of intangible assets subject to amortization as of March 31, 2018 and September 30, 2017 . Core Deposit Intangible Brand Other Total (dollars in thousands) As of March 31, 2018 Gross carrying amount $ 7,339 $ 8,464 $ 538 $ 16,341 Accumulated amortization (2,116 ) (5,546 ) (157 ) (7,819 ) Net intangible assets $ 5,223 $ 2,918 $ 381 $ 8,522 As of September 30, 2017 Gross carrying amount $ 7,339 $ 8,464 $ 538 $ 16,341 Accumulated amortization (1,579 ) (5,264 ) (124 ) (6,967 ) Net intangible assets $ 5,760 $ 3,200 $ 414 $ 9,374
Schedule of estimated amortization expense of intangible assets	Estimated amortization expense of intangible assets in subsequent fiscal years is as follows. Amount (dollars in thousands) Remaining in 2018 $ 810 2019 1,538 2020 1,430 2021 1,334 2022 1,249 2023 and thereafter 2,161 Total $ 8,522

Loan Servicing Rights (Tables)

Loan Servicing Rights (Tables)	6 Months Ended
	Mar. 31, 2018
Transfers and Servicing [Abstract]
Schedule of loan servicing rights and valuation allowance activity	The following table is the activity for loan servicing rights and the related valuation allowance for the three and six months ended March 31, 2018 and 2017 . Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands) Loan servicing rights Beginning of period $ 3,842 $ 5,286 $ 4,155 $ 5,794 Additions — — — — Amortization ¹ (246 ) (380 ) (559 ) (888 ) End of period $ 3,596 $ 4,906 $ 3,596 $ 4,906 Valuation allowance Beginning of period $ (43 ) $ (8 ) $ (81 ) $ (13 ) (Additions) / reductions ¹ 33 5 71 10 End of period $ (10 ) $ (3 ) $ (10 ) $ (3 ) Loan servicing rights, net $ 3,586 $ 4,903 $ 3,586 $ 4,903 Servicing fees received $ 435 $ 525 $ 872 $ 1,073 Balance of loans serviced at: Beginning of period 692,593 823,375 722,461 868,865 End of period 669,767 792,779 669,767 792,779 1 Changes to carrying amounts are reported net of loan servicing income on the consolidated statements of comprehensive income for the periods presented.

Securities Sold Under Agreeme39

Securities Sold Under Agreements to Repurchase (Tables)	6 Months Ended
	Mar. 31, 2018
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Abstract]
Schedule of repurchases agreements	The following tables present the gross obligation by the class of collateral pledged and the remaining contractual maturity of the agreements at March 31, 2018 and September 30, 2017 . March 31, 2018 Remaining Contractual Maturity of the Agreements Overnight and Continuous Up to 30 Days 30-90 Days Greater than 90 Days Total (dollars in thousands) Repurchase agreements Municipal securities $ 3,024 $ — $ — $ — $ 3,024 Mortgage-backed securities 100,267 — — — 100,267 Total repurchase agreements $ 103,291 $ — $ — $ — $ 103,291 September 30, 2017 Remaining Contractual Maturity of the Agreements Overnight and Continuous Up to 30 Days 30-90 Days Greater than 90 Days Total (dollars in thousands) Repurchase agreements Municipal securities $ 3,626 $ — $ — $ — $ 3,626 Mortgage-backed securities 129,010 — — — 129,010 Total repurchase agreements $ 132,636 $ — $ — $ — $ 132,636

FHLB Advances and Other Borro40

FHLB Advances and Other Borrowings (Tables)	6 Months Ended
	Mar. 31, 2018
Federal Home Loan Banks [Abstract]
Schedule of FHLB advances and other borrowings	FHLB advances and other borrowings consist of the following at March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 (dollars in thousands) Short-term borrowings: Notes payable to FHLB, interest rates from 1.76% to 1.80% and matured dates in April 2018, collateralized by real estate loans, with various call dates at the option of the FHLB $ 350,000 $ 512,200 FHLB fed funds advance, interest rate of 1.91% and maturity date in October 2018 75,000 75,000 Long-term borrowings: Notes payable to FHLB, interest rates from 1.05% to 3.66% and maturity dates from April 2018 to July 2023, collateralized by real estate loans, with various call dates at the option of the FHLB 126,000 56,000 Total 551,000 643,200 Fair value adjustment ¹ 3 14 Total FHLB advances and other borrowings $ 551,003 $ 643,214 1 Adjustment reflects the fair value adjustments related to the FHLB advances and notes payable assumed as part of the HF Financial acquisition.
Schedule of FHLB advances and other borrowings by maturity date	As of March 31, 2018 , FHLB advances and other borrowings are due or callable (whichever is earlier) in subsequent fiscal years as follows. Amount (dollars in thousands) Remaining in 2018 $ 381,000 2019 75,000 2020 70,000 2021 — 2022 — 2023 and thereafter 25,000 Total $ 551,000

Subordinated Debentures and S41

Subordinated Debentures and Subordinated Notes Payable (Tables)	6 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Summary of subordinated debentures and subordinated notes payable	Subordinated debentures and subordinated notes payable are summarized as follows. March 31, 2018 September 30, 2017 Amount Outstanding Common Shares Held in Other Assets Amount Outstanding Common Shares Held in Other Assets (dollars in thousands) Junior subordinated debentures payable to nonconsolidated trusts GW Statutory Trust IV, variable rate of 2.85%, plus 3 month LIBOR $ 23,093 $ 693 $ 23,093 $ 693 GW Statutory Trust VI, variable rate of 1.48%, plus 3 month LIBOR 30,928 928 30,928 928 SSB Trust II, variable rate of 1.85%, plus 3 month LIBOR 2,062 62 2,062 62 HF Capital Trust III, variable rate of 3.35%, plus 3 month LIBOR 5,155 155 5,155 155 HF Capital Trust IV, variable rate of 3.10%, plus 3 month LIBOR 7,217 217 7,217 217 HF Capital Trust V, variable rate of 1.83%, plus 3 month LIBOR 5,310 310 5,310 310 HF Capital Trust VI, variable rate of 1.65%, plus 3 month LIBOR 2,155 155 2,155 155 Total junior subordinated debentures payable 75,920 $ 2,520 75,920 $ 2,520 Less: fair value adjustment ¹ (2,363 ) (2,409 ) Total junior subordinated debentures payable, net of fair value adjustment 73,557 73,511 Subordinated notes payable Fixed to floating rate, 4.875% per annum 35,000 35,000 Less: unamortized debt issuance costs (172 ) (209 ) Total subordinated notes payable 34,828 34,791 Total subordinated debentures and subordinated notes payable $ 108,385 $ 108,302 1 Adjustment reflects the fair value adjustments related to the junior subordinated deferrable interest debentures assumed as part of the HF Financial acquisition.

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Mar. 31, 2018
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, 2018 and 2017 . Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands) Currently paid or payable Federal $ 11,791 $ 16,789 $ 20,752 $ 29,942 State 2,939 2,337 5,394 4,701 Total 14,730 19,126 26,146 34,643 Deferred tax expense Federal 74 (1,044 ) 16,838 (566 ) State (85 ) 128 377 194 Total (11 ) (916 ) 17,215 (372 ) Total provision for income taxes $ 14,719 $ 18,210 $ 43,361 $ 34,271
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 of 24.5% for the three and six months ended March 31, 2018 and 35% for the three and six months ended March 31, 2017 to pretax income due to the following. Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands) Income tax expense computed at the statutory rate $ 13,552 $ 18,679 $ 27,748 $ 37,217 Increase (decrease) in income taxes resulting from: State income taxes, net of federal benefit 2,154 1,602 4,356 3,182 Tax exempt interest income (1,415 ) (1,996 ) (2,786 ) (4,034 ) Impact of enacted federal income tax rate reduction — — 13,586 — Other 428 (75 ) 457 (2,094 ) Income tax expense, as reported $ 14,719 $ 18,210 $ 43,361 $ 34,271
Schedule of Deferred Tax Assets and Liabilities	Net deferred tax assets (liabilities) consist of the following components at March 31, 2018 and September 30, 2017 . March 31, 2018 September 30, 2017 (dollars in thousands) Deferred tax assets: Allowance for loan and lease losses $ 16,311 $ 23,730 Compensation 3,246 6,227 Securities available for sale 7,406 3,413 Other real estate owned 505 763 Core deposit intangible and other fair value adjustments 4,235 6,058 Excess tax basis of FDIC indemnification asset and clawback liability 3,574 4,563 Excess tax basis of loans acquired over carrying value 5,959 9,417 Other reserves 2,810 4,406 Other 4,988 6,922 Total deferred tax assets 49,034 65,499 Deferred tax liabilities: Goodwill and other intangibles (11,518 ) (13,784 ) Premises and equipment (5,590 ) (8,828 ) Other (297 ) (487 ) Total deferred tax liabilities (17,405 ) (23,099 ) Net deferred tax assets $ 31,629 $ 42,400

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of restricted share and performance-based stock award activity	The following is a summary of the Plans’ restricted share and performance-based stock award activity as of March 31, 2018 and September 30, 2017 . The number of performance shares granted in the following table are reflected at the amount of achievement of the pre-established targets. March 31, 2018 September 30, 2017 Common Weighted-Average Grant Date Fair Value Common Weighted-Average Grant Date Fair Value Restricted Shares Restricted shares, beginning of fiscal year 180,337 $ 33.06 160,335 $ 26.89 Granted 89,003 41.07 90,363 39.35 Vested (81,999 ) 32.12 (68,293 ) 26.97 Forfeited (1,959 ) 40.30 (2,068 ) 30.91 Canceled — — — — Restricted shares, end of period 185,382 $ 37.25 180,337 $ 33.06 Vested, but not issuable at end of period 39,514 $ 32.90 29,287 $ 30.05 Performance Shares Performance shares, beginning of fiscal year 133,604 $ 33.39 236,185 $ 20.28 Granted 56,149 28.92 137,612 39.43 Vested — — (235,055 ) 18.00 Forfeited (2,178 ) 39.71 (5,138 ) 19.80 Canceled — — — — Performance shares, end of period $ 187,575 $ 35.63 $ 133,604 $ 33.39 Vested, but not issuable at end of period 5,612 $ 18.00 5,612 $ 18.00

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of fair value measurements of 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, 2018 and September 30, 2017 . Fair Value Level 1 Level 2 Level 3 (dollars in thousands) As of March 31, 2018 U.S. Treasury securities $ 177,419 $ 177,419 $ — $ — Mortgage-backed securities 1,060,277 — 1,060,277 — States and political subdivision securities 68,900 — 67,935 965 Other 1,002 — 1,002 — Total securities available for sale $ 1,307,598 $ 177,419 $ 1,129,214 $ 965 Derivatives-assets $ 2,832 $ — $ 2,832 $ — Derivatives-liabilities 1,118 — 1,118 — Fair value loans 920,965 — 920,965 — Fair Value Level 1 Level 2 Level 3 (dollars in thousands) As of September 30, 2017 U.S. Treasury securities $ 228,603 $ 228,603 $ — $ — Mortgage-backed securities 1,065,737 — 1,065,737 — States and political subdivision securities 72,586 — 71,517 1,069 Other 1,034 — 1,034 — Total securities available for sale $ 1,367,960 $ 228,603 $ 1,138,288 $ 1,069 Derivatives-assets $ — $ — $ — $ — Derivatives-liabilities 17,155 — 17,155 — Fair value loans 1,016,576 — 1,016,576 —
Schedule of changes in Level 3 financial instruments	The following table presents the changes in Level 3 financial instruments for the three and six months ended March 31, 2018 and 2017 . Three Months Ended Six Months Ended March 31, 2018 March 31, 2017 March 31, 2018 March 31, 2017 (dollars in thousands) Balance, beginning of period $ 965 $ 1,224 $ 1,069 $ 1,315 Principal paydown — — (104 ) (91 ) Balance, end of period $ 965 $ 1,224 $ 965 $ 1,224
Summary of 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, 2018 and September 30, 2017 . Fair Value Level 1 Level 2 Level 3 (dollars in thousands) As of March 31, 2018 Other repossessed property $ 7,679 $ — $ — $ 7,679 Impaired loans 198,609 — — 198,609 Loans held for sale, at lower of cost or fair value 2,429 — 2,429 — Loan servicing rights 3,586 — — 3,586 Property held for sale 1,109 — — 1,109 As of September 30, 2017 Other repossessed property $ 7,728 $ — $ — $ 7,728 Impaired loans 185,388 — — 185,388 Loans held for sale, at lower of cost or fair value 7,456 — 7,456 — Loan servicing rights 4,074 — — 4,074 Property held for sale 5,147 — — 5,147
Summary of valuation techniques and significant unobservable inputs used to measure Level 3 fair value measurements	The valuation techniques and significant unobservable inputs used to measure Level 3 fair value measurements at March 31, 2018 were as follows. Fair Value of Assets / (Liabilities) at March 31, 2018 Valuation Unobservable Range Weighted (dollars in thousands) Other repossessed property $ 7,679 Appraisal value Property specific adjustment N/A N/A Impaired loans 198,609 Appraisal value Property specific adjustment N/A N/A Loan servicing rights 3,586 Discounted cash flows Constant prepayment rate 7.9 - 20.5% 10.0 - 15.0% 10.4% 11.8% Property held for sale 1,109 Appraisal value Property specific adjustment N/A N/A
Schedule of fair values for balance sheet instruments	Fair values for balance sheet instruments as of March 31, 2018 and September 30, 2017 are as follows. March 31, 2018 September 30, 2017 Level in Fair Value Hierarchy Carrying Amount Fair Carrying Amount Fair (dollars in thousands) Assets Cash and cash equivalents Level 1 $ 371,749 $ 371,749 $ 360,396 $ 360,396 Loans, net excluding fair valued loans and loans held for sale Level 3 8,349,772 8,238,751 7,881,018 7,798,134 Accrued interest receivable Level 2 49,353 49,353 53,176 53,176 Cash surrender value of life insurance policies Level 2 30,032 30,032 29,619 29,619 FHLB stock Level 2 33,720 33,720 37,551 37,551 Liabilities Deposits Level 2 $ 9,386,967 $ 9,384,577 $ 8,977,613 $ 8,978,926 FHLB advances and other borrowings Level 2 551,003 477,292 643,214 645,421 Securities sold under repurchase agreements Level 2 103,291 103,291 132,636 132,636 Accrued interest payable Level 2 6,165 6,165 4,405 4,405 Subordinated debentures and subordinated notes payable Level 2 108,385 107,826 108,302 108,293

Earnings per Share (Tables)

Earnings per Share (Tables)	6 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of basic and diluted earnings per share	The following information was used in the computation of basic and diluted earnings per share (EPS) for the three and six months ended March 31, 2018 and 2017 . Three Months Ended March 31, Six Months Ended March 31, 2018 2017 2018 2017 (dollars in thousands, except per share data) Net income $ 40,532 $ 35,162 $ 69,762 $ 72,065 Weighted average common shares outstanding 58,941,315 58,788,802 58,921,972 58,769,662 Dilutive effect of stock based compensation 204,802 284,867 194,951 263,125 Weighted average common shares outstanding for diluted earnings per share calculation 59,146,117 59,073,669 59,116,923 59,032,787 Basic earnings per share $ 0.69 $ 0.60 $ 1.18 $ 1.23 Diluted earnings per share $ 0.69 $ 0.60 $ 1.18 $ 1.22

Nature of Operations and Summ46

Nature of Operations and Summary of Significant Policies - Narrative (Details) - $ / shares	Apr. 26, 2018	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Dividends Payable [Line Items]
Common stock dividends declared (in dollars per share)		$ 0.20	$ 0.17	$ 0.40	$ 0.34
Subsequent event
Dividends Payable [Line Items]
Common stock dividends declared (in dollars per share)	$ 0.25

Nature of Operations and Summ47

Nature of Operations and Summary of Significant Policies - Prior Period Adjustments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Interest income - loans	$ 109,993	$ 99,481	$ 217,674	$ 199,413	$ 407,282	$ 363,728
Noninterest income - service charges and other fees	$ 12,047	13,574	$ 25,224	27,410	55,725	52,925
As originally reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Interest income - loans		101,136		202,818	414,434	370,444
Noninterest income - service charges and other fees		11,919		24,005	48,573	46,209
Immaterial Classification Error Related To Credit Card Interchange Income | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Interest income - loans		(1,655)		(3,405)	(7,152)	(6,716)
Noninterest income - service charges and other fees		$ 1,655		$ 3,405	$ 7,152	$ 6,716

New Accounting Pronouncements -

New Accounting Pronouncements - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
		Mar. 31, 2018	Mar. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Act - Stranded tax effects	[1]		$ 0
Accumulated Other Comprehensive Loss
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Act - Stranded tax effects		$ (2,400)	(2,353)	[1]
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Act - Stranded tax effects	[1]		$ 2,353
ASU 2018-02 | Accumulated Other Comprehensive Loss
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Act - Stranded tax effects		(2,400)
ASU 2018-02 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Act - Stranded tax effects		$ 2,400
[1]	Reclassification due to adoption of ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. See Note 2, New Accounting Pronouncements and Note 15, Income Taxes, for additional information.

Securities Available for Sale -

Securities Available for Sale - Narrative (Details)	3 Months Ended		6 Months Ended
	Mar. 31, 2018USD ($)security	Mar. 31, 2017USD ($)	Mar. 31, 2018USD ($)security	Mar. 31, 2017USD ($)	Sep. 30, 2017USD ($)security
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales of securities available for sale	$ 25,000,000	$ 5,000,000	$ 25,206,000	$ 5,042,000
Available-for-sale securities, gross realized gains	0	0	0	0
Available-for-sale securities, gross realized losses	0	0	0	0
Other than temporary impairment losses recognized in earnings	0	$ 0	0	$ 0
Securities pledged as collateral	$ 920,600,000		$ 920,600,000		$ 951,400,000
Percentage of investment portfolio in continuous loss position (as a percent)	97.00%		97.00%		68.00%
Number of securities in an unrealized loss position (securities) | security	352		352		249

Securities Available for Sale50

Securities Available for Sale - Schedule of Amortized Cost and Fair Value of Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	$ 1,337,641	$ 1,376,942
Gross Unrealized Gains	204	1,845
Gross Unrealized Losses	(30,247)	(10,827)
Estimated Fair Value	1,307,598	1,367,960
U.S. Treasury securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	178,563	228,039
Gross Unrealized Gains	0	579
Gross Unrealized Losses	(1,144)	(15)
Estimated Fair Value	177,419	228,603
Mortgage-backed securities | Government National Mortgage Association
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	452,297	511,457
Gross Unrealized Gains	47	228
Gross Unrealized Losses	(13,971)	(6,635)
Estimated Fair Value	438,373	505,050
Mortgage-backed securities | Federal Home Loan Mortgage Corporation
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	218,838	169,147
Gross Unrealized Gains	3	75
Gross Unrealized Losses	(4,878)	(1,247)
Estimated Fair Value	213,963	167,975
Mortgage-backed securities | Federal National Mortgage Association
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	179,268	170,247
Gross Unrealized Gains	0	22
Gross Unrealized Losses	(4,591)	(1,287)
Estimated Fair Value	174,677	168,982
Mortgage-backed securities | Small Business Assistance Program
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	237,156	224,005
Gross Unrealized Gains	144	726
Gross Unrealized Losses	(4,036)	(1,001)
Estimated Fair Value	233,264	223,730
States and political subdivision securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	70,513	73,041
Gross Unrealized Gains	10	187
Gross Unrealized Losses	(1,623)	(642)
Estimated Fair Value	68,900	72,586
Other
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	1,006	1,006
Gross Unrealized Gains	0	28
Gross Unrealized Losses	(4)	0
Estimated Fair Value	$ 1,002	$ 1,034

Securities Available for Sale51

Securities Available for Sale - Schedule of Amortized Cost and Fair Value of Investments by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Amortized Cost
Due in one year or less	$ 43,291	$ 91,535
Due after one year through five years	189,787	193,117
Due after five years through ten years	15,876	16,306
Due after ten years	122	122
Amortized Cost	249,076	301,080
Estimated Fair Value
Due in one year or less	43,204	91,597
Due after one year through five years	187,741	193,373
Due after five years through ten years	15,252	16,097
Due after ten years	122	122
Estimated Fair Value	246,319	301,189
Amortized Cost	1,337,641	1,376,942
Estimated Fair Value	1,307,598	1,367,960
Securities without contractual maturities, Amortized Cost	1,006	1,006
Securities without contractual maturities, Fair Value	1,002	1,034
Mortgage-backed securities
Estimated Fair Value
Amortized Cost	1,087,559	1,074,856
Estimated Fair Value	$ 1,060,277	$ 1,065,737

Securities Available for Sale52

Securities Available for Sale - Schedule of Gross Unrealized Losses on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Estimated Fair Value	$ 478,378	$ 667,677
12 months or more, Estimated Fair Value	790,818	267,141
Estimated Fair Value	1,269,196	934,818
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized Losses	(5,751)	(5,637)
12 months or more, Unrealized Losses	(24,496)	(5,190)
Unrealized Losses	(30,247)	(10,827)
U.S. Treasury securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Estimated Fair Value	148,360	10,003
12 months or more, Estimated Fair Value	29,059	0
Estimated Fair Value	177,419	10,003
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized Losses	(873)	(15)
12 months or more, Unrealized Losses	(271)	0
Unrealized Losses	(1,144)	(15)
Mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Estimated Fair Value	314,049	635,969
12 months or more, Estimated Fair Value	712,510	241,368
Estimated Fair Value	1,026,559	877,337
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized Losses	(4,765)	(5,425)
12 months or more, Unrealized Losses	(22,711)	(4,746)
Unrealized Losses	(27,476)	(10,171)
States and political subdivision securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Estimated Fair Value	14,967	21,705
12 months or more, Estimated Fair Value	49,249	25,773
Estimated Fair Value	64,216	47,478
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized Losses	(109)	(197)
12 months or more, Unrealized Losses	(1,514)	(444)
Unrealized Losses	(1,623)	(641)
Other
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, Estimated Fair Value	1,002	0
12 months or more, Estimated Fair Value	0	0
Estimated Fair Value	1,002	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 months, Unrealized Losses	(4)	0
12 months or more, Unrealized Losses	0	0
Unrealized Losses	$ (4)	$ 0

Loans - Narrative (Details)

Loans - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans covered by FDIC loss share agreements	$ 50,727		$ 50,727		$ 57,537
Loan held for sale	2,429		2,429		7,456
Loans and written loan commitments at fair value under the fair value option	920,965		920,965		1,016,576
Unamortized discount on acquired loans	13,100		13,100		11,600
Loans in process	1,500		1,500		(800)
Loans guaranteed by U.S. Government Agencies	8,267,966		8,267,966		7,787,016
Principal balances of residential real estate loans sold	67,600	$ 53,400	117,800	$ 145,100
Loans greater than 90 days past due and still accruing interest	900		900		1,900
Valuation adjustments made to repossessed properties	700	500	700	900
Specific reserves included in the allowance for loan losses for TDRs	10,000		10,000		8,800
Troubled debt restructuring, commitments to lend additional funds	700		700		0
Transfers out of troubled debt restructuring status	100	$ 2,100	600	$ 2,100
Loans Guaranteed by US Government Authorities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans guaranteed by U.S. Government Agencies	$ 170,300		$ 170,300		$ 168,300

Loans - Schedule of Loans Recei

Loans - Schedule of Loans Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	$ 9,376,373	$ 9,008,515
Less: Unamortized discount on acquired loans	(23,501)	(29,121)
Unearned net deferred fees and costs and loans in process	(14,566)	(10,841)
Net loans	9,338,306	8,968,553
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	4,467,778	4,124,805
Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	2,177,020	2,122,138
Commercial non-real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	1,767,587	1,718,914
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	866,982	932,892
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	55,190	66,559
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	$ 41,816	$ 43,207

Loans - Schedule of the Company

Loans - Schedule of the Company's Nonaccrual Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	$ 127,393	$ 132,225
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	26,343	14,693
Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	86,758	99,325
Commercial non-real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	10,146	13,674
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	4,058	4,421
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans, excluding loans covered under FDIC loss-sharing arrangements	$ 88	$ 112

Loans - Schedule of the Composi

Loans - Schedule of the Composition of the Loan Portfolio by Internal Risk Rating (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	$ 8,381,180	$ 7,905,281
Loans covered by FDIC loss share agreements	50,727	57,537
Total	8,431,907	7,962,818
Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	7,910,057	7,429,041
Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	254,686	273,825
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	213,437	197,692
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	3,000	4,723
Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	4,013,720	3,638,032
Loans covered by FDIC loss share agreements	0	0
Total	4,013,720	3,638,032
Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	3,888,128	3,519,689
Commercial real estate | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	62,695	80,195
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	62,784	37,627
Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	113	521
Commercial real estate | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Agriculture
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	1,959,877	1,865,882
Loans covered by FDIC loss share agreements	0	0
Total	1,959,877	1,865,882
Agriculture | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	1,683,280	1,577,403
Agriculture | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	152,878	157,407
Agriculture | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	123,714	130,953
Agriculture | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	5	119
Agriculture | 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	1,499,891	1,426,960
Loans covered by FDIC loss share agreements	0	0
Total	1,499,891	1,426,960
Commercial non-real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	1,443,731	1,369,803
Commercial non-real estate | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	33,852	31,878
Commercial non-real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	19,552	21,438
Commercial non-real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	2,756	3,841
Commercial non-real estate | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	810,991	865,034
Loans covered by FDIC loss share agreements	50,727	57,537
Total	861,718	922,571
Residential real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	798,778	853,266
Residential real estate | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	4,935	4,158
Residential real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	7,152	7,368
Residential real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	126	242
Residential real estate | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	54,885	66,166
Loans covered by FDIC loss share agreements	0	0
Total	54,885	66,166
Consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	54,324	65,673
Consumer | Watchlist
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	326	187
Consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	235	306
Consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Consumer | Loss
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	0	0
Other
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	41,816	43,207
Loans covered by FDIC loss share agreements	0	0
Total	41,816	43,207
Other | Pass
Financing Receivable, Recorded Investment [Line Items]
Total financing receivables	41,816	43,207
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 - Schedule of Past Due Lo

Loans - Schedule of Past Due Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	$ 8,381,180	$ 7,905,281
Loans covered by FDIC loss sharing agreements	50,727	57,537
Total	8,431,907	7,962,818
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	4,013,720	3,638,032
Loans covered by FDIC loss sharing agreements	0	0
Total	4,013,720	3,638,032
Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	1,959,877	1,865,882
Loans covered by FDIC loss sharing agreements	0	0
Total	1,959,877	1,865,882
Commercial non-real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	1,499,891	1,426,960
Loans covered by FDIC loss sharing agreements	0	0
Total	1,499,891	1,426,960
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	810,991	865,034
Loans covered by FDIC loss sharing agreements	50,727	57,537
Total	861,718	922,571
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	54,885	66,166
Loans covered by FDIC loss sharing agreements	0	0
Total	54,885	66,166
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	41,816	43,207
Loans covered by FDIC loss sharing agreements	0	0
Total	41,816	43,207
Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	69,237	69,142
Loans covered by FDIC loss sharing agreements	2,088	1,790
Total	71,325	70,932
Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	25,694	29,916
Past Due | Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	29,256	25,478
Past Due | Commercial non-real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	10,078	11,180
Past Due | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	4,022	2,455
Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	187	113
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	12,068	6,313
Loans covered by FDIC loss sharing agreements	1,283	998
Total	13,351	7,311
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	3,308	876
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	2,387	1,453
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	3,665	2,485
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	2,568	1,428
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	140	71
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	1,721	25,932
Loans covered by FDIC loss sharing agreements	217	54
Total	1,938	25,986
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	67	22,536
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	371	3,181
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	1,190	115
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	90	76
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	3	24
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 | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	55,448	36,897
Loans covered by FDIC loss sharing agreements	588	738
Total	56,036	37,635
Past Due | 90 Days or Greater Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	22,319	6,504
Past Due | 90 Days or Greater Past Due | Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	26,498	20,844
Past Due | 90 Days or Greater Past Due | Commercial non-real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	5,223	8,580
Past Due | 90 Days or Greater Past Due | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	1,364	951
Past Due | 90 Days or Greater Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	44	18
Past Due | 90 Days or Greater Past Due | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	0	0
Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	8,311,943	7,836,139
Loans covered by FDIC loss sharing agreements	48,639	55,747
Total	8,360,582	7,891,886
Current | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	3,988,026	3,608,116
Current | Agriculture
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	1,930,621	1,840,404
Current | Commercial non-real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	1,489,813	1,415,780
Current | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	806,969	862,579
Current | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	54,698	66,053
Current | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables, net of unamortized discount on acquired loans	$ 41,816	$ 43,207

Loans - Schedule of Impaired Lo

Loans - Schedule of Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
With an allowance recorded:
Recorded Investment	$ 131,997		$ 131,997		$ 123,445
Unpaid Principal Balance	147,978		147,978		148,077
Related Allowance	24,656		24,656		22,535
With no allowance recorded:
Recorded Investment	91,268		91,268		84,478
Unpaid Principal Balance	148,095		148,095		183,341
Total Recorded Investment, Impaired Loans	223,265		223,265		207,923
Total Unpaid Principal Balance, Impaired Loans	296,073		296,073		331,418
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	225,805	$ 229,984	219,845	$ 225,464
Interest Income Recognized While on Impaired Status	2,111	2,367	5,289	5,455
Commercial real estate
With an allowance recorded:
Recorded Investment	48,532		48,532		20,819
Unpaid Principal Balance	49,799		49,799		24,893
Related Allowance	7,248		7,248		3,621
With no allowance recorded:
Recorded Investment	13,335		13,335		16,652
Unpaid Principal Balance	52,866		52,866		69,677
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	66,577	44,807	56,875	47,873
Interest Income Recognized While on Impaired Status	477	545	2,053	1,215
Agriculture
With an allowance recorded:
Recorded Investment	63,293		63,293		79,219
Unpaid Principal Balance	73,823		73,823		88,268
Related Allowance	10,465		10,465		11,468
With no allowance recorded:
Recorded Investment	61,643		61,643		51,256
Unpaid Principal Balance	66,567		66,567		64,177
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	121,062	128,919	124,200	119,892
Interest Income Recognized While on Impaired Status	1,189	1,326	2,171	3,193
Commercial non-real estate
With an allowance recorded:
Recorded Investment	14,747		14,747		17,950
Unpaid Principal Balance	18,140		18,140		28,755
Related Allowance	4,320		4,320		4,779
With no allowance recorded:
Recorded Investment	14,110		14,110		13,983
Unpaid Principal Balance	23,372		23,372		38,924
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	30,350	46,304	30,878	47,477
Interest Income Recognized While on Impaired Status	325	358	776	780
Residential real estate
With an allowance recorded:
Recorded Investment	5,208		5,208		5,177
Unpaid Principal Balance	5,991		5,991		5,874
Related Allowance	2,549		2,549		2,581
With no allowance recorded:
Recorded Investment	2,166		2,166		2,574
Unpaid Principal Balance	5,157		5,157		9,613
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	7,578	9,565	7,636	9,831
Interest Income Recognized While on Impaired Status	116	126	281	240
Consumer
With an allowance recorded:
Recorded Investment	217		217		280
Unpaid Principal Balance	225		225		287
Related Allowance	74		74		86
With no allowance recorded:
Recorded Investment	14		14		13
Unpaid Principal Balance	133		133		$ 950
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	238	389	256	391
Interest Income Recognized While on Impaired Status	$ 4	$ 12	$ 8	$ 27

Loans - Summary of Troubled Deb

Loans - Summary of Troubled Debt Restructurings on Accruing and Nonaccrual Financing Receivables (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018USD ($)contract	Mar. 31, 2017USD ($)contract	Mar. 31, 2018USD ($)contract	Mar. 31, 2017USD ($)contract	Sep. 30, 2017USD ($)
Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 37,796		$ 37,796		$ 32,490
Financing receivable, modifications, number of contracts | contract	3	4	3	7
Financing receivable, modifications, pre-modification recorded investment	$ 6,146	$ 8,527	$ 6,146	$ 8,969
Financing receivable, modifications, post-modification recorded investment	$ 6,146	$ 8,527	$ 6,146	$ 8,969
Change in recorded investment due to principal paydown at time of modification, number of contracts | contract	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 | contract	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
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 67,385		$ 67,385		71,334
Financing receivable, modifications, number of contracts | contract	6	9	6	10
Financing receivable, modifications, pre-modification recorded investment	$ 8,374	$ 13,009	$ 8,374	$ 13,030
Financing receivable, modifications, post-modification recorded investment	$ 8,374	$ 13,009	$ 8,374	$ 13,030
Change in recorded investment due to principal paydown at time of modification, number of contracts | contract	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 | contract	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
Commercial real estate | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 617		$ 617		1,121
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 2,632		$ 2,632		5,351
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial real estate | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Agriculture | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 29,200		$ 29,200		22,678
Financing receivable, modifications, number of contracts | contract	2	2	2	2
Financing receivable, modifications, pre-modification recorded investment	$ 6,073	$ 8,434	$ 6,073	$ 8,434
Financing receivable, modifications, post-modification recorded investment	$ 6,073	$ 8,434	$ 6,073	$ 8,434
Agriculture | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	1	0	1	0
Financing receivable, modifications, pre-modification recorded investment	$ 5,500	$ 0	$ 5,500	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 5,500	$ 0	$ 5,500	$ 0
Agriculture | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	2	0	2
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 8,434	$ 0	$ 8,434
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 8,434	$ 0	$ 8,434
Agriculture | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	1	0	1	0
Financing receivable, modifications, pre-modification recorded investment	$ 573	$ 0	$ 573	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 573	$ 0	$ 573	$ 0
Agriculture | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Agriculture | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Agriculture | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 60,098		$ 60,098		59,633
Financing receivable, modifications, number of contracts | contract	6	6	6	6
Financing receivable, modifications, pre-modification recorded investment	$ 8,374	$ 12,988	$ 8,374	$ 12,988
Financing receivable, modifications, post-modification recorded investment	$ 8,374	$ 12,988	$ 8,374	$ 12,988
Agriculture | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Agriculture | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	3	6	3	6
Financing receivable, modifications, pre-modification recorded investment	$ 6,324	$ 12,988	$ 6,324	$ 12,988
Financing receivable, modifications, post-modification recorded investment	$ 6,324	$ 12,988	$ 6,324	$ 12,988
Agriculture | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	3	0	3	0
Financing receivable, modifications, pre-modification recorded investment	$ 2,050	$ 0	$ 2,050	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 2,050	$ 0	$ 2,050	$ 0
Agriculture | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Agriculture | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 7,647		$ 7,647		8,369
Financing receivable, modifications, number of contracts | contract	0	2	0	4
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 93	$ 0	$ 526
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 93	$ 0	$ 526
Commercial non-real estate | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	2	0	4
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 93	$ 0	$ 526
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 93	$ 0	$ 526
Commercial non-real estate | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 3,916		$ 3,916		5,641
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Commercial non-real estate | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Residential real estate | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 249		$ 249		311
Financing receivable, modifications, number of contracts | contract	0	0	0	1
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0	$ 9
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0	$ 9
Residential real estate | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Residential real estate | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Residential real estate | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0	1
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0	$ 9
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0	$ 9
Residential real estate | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Residential real estate | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Residential real estate | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 739		$ 739		688
Financing receivable, modifications, number of contracts | contract	0	0	0	1
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0	$ 21
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0	$ 21
Residential real estate | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Residential real estate | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Residential real estate | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0	1
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0	$ 21
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0	$ 21
Residential real estate | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Residential real estate | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Consumer | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 83		$ 83		11
Financing receivable, modifications, number of contracts | contract	1	0	1	0
Financing receivable, modifications, pre-modification recorded investment	$ 73	$ 0	$ 73	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 73	$ 0	$ 73	$ 0
Consumer | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	1	0	1	0
Financing receivable, modifications, pre-modification recorded investment	$ 73	$ 0	$ 73	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 73	$ 0	$ 73	$ 0
Consumer | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Consumer | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Consumer | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Consumer | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Consumer | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 0		$ 0		$ 21
Financing receivable, modifications, number of contracts | contract	0	3	0	3
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 21	$ 0	$ 21
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 21	$ 0	$ 21
Consumer | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Consumer | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	3	0	3
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 21	$ 0	$ 21
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 21	$ 0	$ 21
Consumer | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Consumer | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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
Consumer | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	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

Loans - Subsequent Defaults on

Loans - Subsequent Defaults on Modified Loans (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018USD ($)contract	Mar. 31, 2017USD ($)contract	Mar. 31, 2018USD ($)contract	Mar. 31, 2017USD ($)contract
Financing Receivable, Modifications [Line Items]
Number of Loans | contract	3	1	5	2
Recorded Investment | $	$ 4,264	$ 0	$ 6,023	$ 34
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Loans | contract	0	0	1	1
Recorded Investment | $	$ 0	$ 0	$ 1,012	$ 34
Agriculture
Financing Receivable, Modifications [Line Items]
Number of Loans | contract	3	0	4	0
Recorded Investment | $	$ 4,264	$ 0	$ 5,011	$ 0
Commercial non-real estate
Financing Receivable, Modifications [Line Items]
Number of Loans | contract	0	1	0	1
Recorded Investment | $	$ 0	$ 0	$ 0	$ 0
Residential real estate
Financing Receivable, Modifications [Line Items]
Number of Loans | contract	0	0	0	0
Recorded Investment | $	$ 0	$ 0	$ 0	$ 0
Consumer
Financing Receivable, Modifications [Line Items]
Number of Loans | contract	0	0	0	0
Recorded Investment | $	$ 0	$ 0	$ 0	$ 0

Allowance for Loan and Lease 61

Allowance for Loan and Lease Losses - Summary of Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	$ 64,023	$ 66,767	$ 63,503	$ 64,642
Charge-offs	(4,295)	(9,079)	(8,904)	(14,631)
Recoveries	511	988	1,083	1,616
Provision	4,996	5,060	9,600	12,010
Allowance for loan losses, ending balance	65,139	62,685	65,139	62,685
Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			993
Recoveries	100	1,100	100	1,000
Impairment (improvement) of ASC 310-30 loans	(96)	(1,051)	(143)	(952)
Allowance for loan losses, ending balance	834		834
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	15,995	16,623	16,941	17,946
Charge-offs	(1,268)	(1,824)	(1,597)	(1,824)
Recoveries	61	286	209	385
Provision	4,077	2,096	3,322	549
Allowance for loan losses, ending balance	18,914	16,996	18,914	16,996
Commercial real estate | Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			682
Impairment (improvement) of ASC 310-30 loans	49	(185)	39	(60)
Allowance for loan losses, ending balance	716		716
Agriculture
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	24,750	28,519	25,757	25,115
Charge-offs	(783)	(4,554)	(2,981)	(7,420)
Recoveries	125	118	172	144
Provision	152	2,237	1,296	8,481
Allowance for loan losses, ending balance	24,129	26,320	24,129	26,320
Agriculture | Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			115
Impairment (improvement) of ASC 310-30 loans	(115)	0	(115)	0
Allowance for loan losses, ending balance	0		0
Commercial non-real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	16,434	13,443	14,114	12,990
Charge-offs	(1,605)	(1,734)	(2,844)	(3,693)
Recoveries	88	121	209	219
Provision	813	119	4,251	2,433
Allowance for loan losses, ending balance	15,730	11,949	15,730	11,949
Commercial non-real estate | Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			0
Impairment (improvement) of ASC 310-30 loans	0	0	0	0
Allowance for loan losses, ending balance	0		0
Residential real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	5,475	6,786	5,347	7,106
Charge-offs	(20)	(117)	(275)	(267)
Recoveries	27	56	117	262
Provision	(341)	210	(11)	(140)
Allowance for loan losses, ending balance	5,111	6,069	5,111	6,069
Residential real estate | Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			196
Impairment (improvement) of ASC 310-30 loans	(30)	(866)	(67)	(892)
Allowance for loan losses, ending balance	118		118
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	307	340	329	438
Charge-offs	(62)	(31)	(116)	(110)
Recoveries	20	15	42	30
Provision	14	47	24	13
Allowance for loan losses, ending balance	279	371	279	371
Consumer | Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			0
Impairment (improvement) of ASC 310-30 loans	0	0	0	0
Allowance for loan losses, ending balance	0		0
Other
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	1,062	1,056	1,015	1,047
Charge-offs	(557)	(819)	(1,091)	(1,317)
Recoveries	190	392	334	576
Provision	281	351	718	674
Allowance for loan losses, ending balance	976	980	976	980
Other | Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance			0
Impairment (improvement) of ASC 310-30 loans	0	$ 0	0	$ 0
Allowance for loan losses, ending balance	$ 0		$ 0

Allowance for Loan and Lease 62

Allowance for Loan and Lease Losses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and written loan commitments at fair value under the fair value option	$ 920,965		$ 920,965			$ 1,016,576
Loan held for sale	2,429		2,429			7,456
Loans guaranteed by U.S. Government Agencies	8,267,966		8,267,966			7,787,016
Allowance for loan leases	65,139	$ 62,685	65,139	$ 62,685	$ 64,023	63,503	$ 66,767	$ 64,642
Net reversal of provision	511	988	1,083	1,616
Unfunded loan commitment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reserve for unfunded loan commitments	500		500			500
(Impairment) improvement of ASC 310-30 loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans guaranteed by U.S. Government Agencies	80,950		80,950			92,595
Allowance for loan leases	834		834			993
Net reversal of provision	100	$ 1,100	100	$ 1,000
Loans Guaranteed by US Government Authorities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans guaranteed by U.S. Government Agencies	170,300		170,300			168,300
Loans Guaranteed by US Government Authorities | Loans and Leases with Allowance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans guaranteed by U.S. Government Agencies	$ 161,500		$ 161,500			$ 168,300

Allowance for Loan and Lease 63

Allowance for Loan and Lease Losses - Summary of Allowance for Loan Losses by Type (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Allowance for loan and lease losses
Individually evaluated for impairment	$ 24,656		$ 22,535
Collectively evaluated for impairment	39,649		39,975
Total allowance	65,139	$ 64,023	63,503	$ 62,685	$ 66,767	$ 64,642
Financing Receivables
Individually evaluated for impairment	223,265		207,923
Collectively evaluated for impairment	7,963,751		7,486,498
Loans Outstanding	8,267,966		7,787,016
Acquired receivables subject to ASC 310-30
Allowance for loan and lease losses
Total allowance	834		993
Financing Receivables
Loans Outstanding	80,950		92,595
Commercial real estate
Allowance for loan and lease losses
Individually evaluated for impairment	7,248		3,621
Collectively evaluated for impairment	10,950		12,638
Total allowance	18,914	15,995	16,941	16,996	16,623	17,946
Financing Receivables
Individually evaluated for impairment	61,867		37,471
Collectively evaluated for impairment	3,846,737		3,487,232
Loans Outstanding	3,937,098		3,554,802
Commercial real estate | Acquired receivables subject to ASC 310-30
Allowance for loan and lease losses
Total allowance	716		682
Financing Receivables
Loans Outstanding	28,494		30,099
Agriculture
Allowance for loan and lease losses
Individually evaluated for impairment	10,465		11,468
Collectively evaluated for impairment	13,664		14,174
Total allowance	24,129	24,750	25,757	26,320	28,519	25,115
Financing Receivables
Individually evaluated for impairment	124,936		130,475
Collectively evaluated for impairment	1,808,883		1,702,634
Loans Outstanding	1,936,565		1,840,283
Agriculture | Acquired receivables subject to ASC 310-30
Allowance for loan and lease losses
Total allowance	0		115
Financing Receivables
Loans Outstanding	2,746		7,174
Commercial non-real estate
Allowance for loan and lease losses
Individually evaluated for impairment	4,320		4,779
Collectively evaluated for impairment	11,410		9,335
Total allowance	15,730	16,434	14,114	11,949	13,443	12,990
Financing Receivables
Individually evaluated for impairment	28,857		31,933
Collectively evaluated for impairment	1,407,897		1,333,888
Loans Outstanding	1,438,985		1,367,741
Commercial non-real estate | Acquired receivables subject to ASC 310-30
Allowance for loan and lease losses
Total allowance	0		0
Financing Receivables
Loans Outstanding	2,231		1,920
Residential real estate
Allowance for loan and lease losses
Individually evaluated for impairment	2,549		2,581
Collectively evaluated for impairment	2,444		2,570
Total allowance	5,111	5,475	5,347	6,069	6,786	7,106
Financing Receivables
Individually evaluated for impairment	7,374		7,751
Collectively evaluated for impairment	804,298		854,330
Loans Outstanding	858,617		914,817
Residential real estate | Acquired receivables subject to ASC 310-30
Allowance for loan and lease losses
Total allowance	118		196
Financing Receivables
Loans Outstanding	46,945		52,736
Consumer
Allowance for loan and lease losses
Individually evaluated for impairment	74		86
Collectively evaluated for impairment	205		243
Total allowance	279	307	329	371	340	438
Financing Receivables
Individually evaluated for impairment	231		293
Collectively evaluated for impairment	54,120		65,207
Loans Outstanding	54,885		66,166
Consumer | Acquired receivables subject to ASC 310-30
Allowance for loan and lease losses
Total allowance	0		0
Financing Receivables
Loans Outstanding	534		666
Other
Allowance for loan and lease losses
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	976		1,015
Total allowance	976	$ 1,062	1,015	$ 980	$ 1,056	$ 1,047
Financing Receivables
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	41,816		43,207
Loans Outstanding	41,816		43,207
Other | Acquired receivables subject to ASC 310-30
Allowance for loan and lease losses
Total allowance	0		0
Financing Receivables
Loans Outstanding	$ 0		$ 0

Accounting for Certain Loans 64

Accounting for Certain Loans Acquired with Deteriorated Credit Quality - Schedule of Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	$ 41,918	$ 39,758	$ 44,131	$ 38,124
Accretion	(3,664)	(3,040)	(7,045)	(5,978)
Reclassification from nonaccretable difference	(413)	1,987	755	6,559
Balance at end of period	$ 37,841	$ 38,705	$ 37,841	$ 38,705

Accounting for Certain Loans 65

Accounting for Certain Loans Acquired with Deteriorated Credit Quality - Schedule of Impaired Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	$ 177,297	$ 193,864
Recorded Investment	80,950	92,595
Carrying Value	80,116	91,602
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	105,489	110,797
Recorded Investment	28,494	30,099
Carrying Value	27,778	29,417
Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	5,813	10,463
Recorded Investment	2,746	7,174
Carrying Value	2,746	7,059
Commercial non-real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	10,001	9,825
Recorded Investment	2,231	1,920
Carrying Value	2,231	1,920
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	55,326	61,981
Recorded Investment	46,945	52,736
Carrying Value	46,827	52,540
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance	668	798
Recorded Investment	534	666
Carrying Value	$ 534	$ 666

FDIC Indemnification Asset - Su

FDIC Indemnification Asset - Summary of FDIC Indemnification Asset Activity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
FDIC Indemnification Asset [Roll Forward]
Balance at beginning of period	$ 4,692	$ 9,887	$ 5,704	$ 10,777
Amortization	(671)	(1,114)	(1,689)	(1,981)
Changes in expected reimbursements from FDIC for changes in expected credit losses	(76)	(133)	(94)	(105)
Changes in reimbursable expenses	(456)	(299)	(662)	(538)
Reimbursements of covered losses to the FDIC	189	30	419	218
Balance at end of period	$ 3,678	$ 8,371	$ 3,678	$ 8,371

Derivative Financial Instrume67

Derivative Financial Instruments - Schedule of Derivative Positions, Notional Amounts and Estimated Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Derivative [Line Items]
Gross Asset Fair Value	$ 18,790	$ 1,850
Gross Liability Fair Value	(8,058)	(19,005)
Not Designated as Hedging Instruments
Derivative [Line Items]
Notional Amount	1,212,603	1,142,939
Gross Asset Fair Value	18,790	5,630
Gross Liability Fair Value	(8,058)	(22,785)
Not Designated as Hedging Instruments | Interest rate swaps | Financial institution counterparties
Derivative [Line Items]
Notional Amount	1,039,100	1,025,474
Gross Asset Fair Value	17,185	4,967
Gross Liability Fair Value	(6,943)	(22,737)
Not Designated as Hedging Instruments | Interest rate swaps | Customer counterparties
Derivative [Line Items]
Notional Amount	118,606	36,072
Gross Asset Fair Value	1,602	615
Gross Liability Fair Value	(1,112)	0
Not Designated as Hedging Instruments | Mortgage loan commitments
Derivative [Line Items]
Notional Amount	27,499	37,765
Gross Asset Fair Value	3	0
Gross Liability Fair Value	0	(48)
Not Designated as Hedging Instruments | Mortgage loan forward sale contracts
Derivative [Line Items]
Notional Amount	27,398	43,628
Gross Asset Fair Value	0	48
Gross Liability Fair Value	$ (3)	$ 0

Derivative Financial Instrume68

Derivative Financial Instruments - Summary of Offsetting Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative assets, gross amount	$ 18,790	$ 1,850
Derivative assets, fair value offset amount	(6,943)	(1,850)
Derivative assets, cash collateral	(9,015)	0
Derivative financial assets, net amount presented in Consolidated Balance Sheets	2,832	0
Derivative liabilities, gross amount	(8,058)	(19,005)
Derivative liabilities, fair value offset amount	6,943	1,850
Derivative liabilities, cash collateral	(3)	0
Derivative financial liabilities, net amount presented in Consolidated Balance Sheets	(1,118)	(17,155)
Security collateral	$ 5,000	25,000
Collateral held for initial margin		$ 2,300

Derivative Financial Instrume69

Derivative Financial Instruments - Effect on the Consolidated Statement of Comprehensive Income (Details) - Noninterest income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Interest rate swaps
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Statements of Income	$ 14,282	$ 1,592	$ 21,509	$ 60,568
Mortgage loan commitments
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Statements of Income	2	158	3	53
Mortgage loan forward sale contracts
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Statements of Income	$ (2)	$ (158)	$ (3)	$ (53)

The Fair Value Option for Cer70

The Fair Value Option for Certain Loans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Eligible item for the fair value option	$ (21)		$ (21)		$ 8.8
Loans greater than 90 days past due or in nonaccrual status	13.3		13.3		14.7
Unpaid principal balance greater than 90 days past due or in nonaccrual status	14.8		14.8		17
Long-term loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total unpaid principal balance of long-term loans	942		942		$ 1,010
Eligible item for the fair value option	$ 1.4	$ 0.3	$ 0.3	$ 0.3

The Fair Value Option for Cer71

The Fair Value Option for Certain Loans - Summary of the Fair Value Option (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of loans	$ (14,838)	$ (5,216)	$ (23,502)	$ (69,218)
Long-term loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of loans	(14,838)	(5,216)	(23,502)	(69,218)
Long-term loans | Noninterest Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of loans	$ (14,838)	$ (5,216)	$ (23,502)	$ (69,218)

Core Deposits and Other Intan72

Core Deposits and Other Intangibles - Intangible Assets Amortization Expense (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 16,341	$ 16,341
Accumulated amortization	(7,819)	(6,967)
Total	8,522	9,374
Core Deposit Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	7,339	7,339
Accumulated amortization	(2,116)	(1,579)
Total	5,223	5,760
Brand Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	8,464	8,464
Accumulated amortization	(5,546)	(5,264)
Total	2,918	3,200
Other Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	538	538
Accumulated amortization	(157)	(124)
Total	$ 381	$ 414

Core Deposits and Other Intan73

Core Deposits and Other Intangibles - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of core deposits and other intangibles	$ 0.4	$ 0.6	$ 0.9	$ 1.4

Core Deposits and Other Intan74

Core Deposits and Other Intangibles - Schedule of Future Amortization Expense (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Remaining in 2018	$ 810
2,019	1,538
2,020	1,430
2,021	1,334
2,022	1,249
2023 and thereafter	2,161
Total	$ 8,522	$ 9,374

Loan Servicing Rights - Schedul

Loan Servicing Rights - Schedule of Loan Servicing Rights Activity and Valuation Allowance (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Loan servicing rights
Beginning of period	$ 3,842	$ 5,286	$ 4,155	$ 5,794
Additions	0	0	0	0
Amortization	(246)	(380)	(559)	(888)
End of period	3,596	4,906	3,596	4,906
Valuation Allowance for Impairment of Recognized Servicing Assets [Roll Forward]
Beginning of period	(43)	(8)	(81)	(13)
(Additions) / reductions	33	5	71	10
End of period	(10)	(3)	(10)	(3)
Loan servicing rights, net	3,586	4,903	3,586	4,903
Servicing fees received	435	525	872	1,073
Balance of loans serviced at:
Beginning of period	692,593	823,375	722,461	868,865
End of period	$ 669,767	$ 792,779	$ 669,767	$ 792,779

Loan Servicing Rights - Narrati

Loan Servicing Rights - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Transfers and Servicing [Abstract]
Constant prepayment rates (as a percent)	10.40%
Discount rate (as a percent)	11.90%
Loan servicing rights, valuation allowance	$ 10	$ 43	$ 81	$ 3	$ 8	$ 13

Securities Sold Under Agreeme77

Securities Sold Under Agreements to Repurchase - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2018	Sep. 30, 2017
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Abstract]
Securities sold under agreements to repurchase	$ 131.2	$ 139.3
Securities sold under agreements to repurchase, fair value of collateral	$ 126.7	$ 137.4
Securities sold under agreements to repurchase, collateral, percentage of borrowed funds (as a percent)	102.00%

Securities Sold Under Agreeme78

Securities Sold Under Agreements to Repurchase - Maturity Schedule of Agreements (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	$ 103,291	$ 132,636
Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	3,024	3,626
Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	100,267	129,010
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	103,291	132,636
Overnight and Continuous | Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	3,024	3,626
Overnight and Continuous | Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	100,267	129,010
Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
Up to 30 Days | Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
Up to 30 Days | Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
30-90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
30-90 Days | Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
30-90 Days | Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
Greater than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
Greater than 90 Days | Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
Greater than 90 Days | Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	$ 0	$ 0

FHLB Advances and Other Borro79

FHLB Advances and Other Borrowings - Schedule of Advances, Related Party Notes (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Total	$ 551,000	$ 643,200
Fair value adjustment	3	14
Total FHLB advances and other borrowings	551,003	643,214
Notes payable to banks
Debt Instrument [Line Items]
Federal Home Loan Bank (FHLB) notes payable and fed funds advance	$ 126,000	56,000
Notes payable to banks | Minimum
Debt Instrument [Line Items]
Stated interest rate (as a percent)	1.05%
Notes payable to banks | Maximum
Debt Instrument [Line Items]
Stated interest rate (as a percent)	3.66%
Notes payable to banks
Debt Instrument [Line Items]
Federal Home Loan Bank (FHLB) notes payable and fed funds advance	$ 350,000	512,200
Notes payable to banks | Minimum
Debt Instrument [Line Items]
Stated interest rate (as a percent)	1.76%
Notes payable to banks | Maximum
Debt Instrument [Line Items]
Stated interest rate (as a percent)	1.80%
Federal Home Loan Bank fed funds advance
Debt Instrument [Line Items]
Interest rate (as a percent)	1.91%
Federal Home Loan Bank (FHLB) notes payable and fed funds advance	$ 75,000	$ 75,000

FHLB Advances and Other Borro80

FHLB Advances and Other Borrowings - Narrative (Details) - USD ($)	6 Months Ended
	Mar. 31, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Current borrowing capacity	$ 1,470,000,000	$ 1,550,000,000
Loans pledged to the Federal Home Loan Bank	3,750,000,000	3,710,000,000
Revolving Credit Facility
Debt Instrument [Line Items]
Borrowing capacity	$ 10,000,000
Unused capacity fee (as a percent)	0.15%
Interest rate at end of period (as a percent)	3.88%
Outstanding advances	$ 0	0
Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.00%
Revolving Credit Facility | FRB Discount Window Loan
Debt Instrument [Line Items]
Borrowing capacity	$ 1,690,000,000	1,890,000,000
Loans pledged to the Federal Reserve Board Discount Window	2,000,000,000	$ 2,550,000,000
Federal Home Loan Bank | Letter of Credit
Debt Instrument [Line Items]
Borrowing capacity	$ 150,000,000

FHLB Advances and Other Borro81

FHLB Advances and Other Borrowings - Schedule of Due or Callable Notes (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Total	$ 108,385	$ 108,302
FHLB Advances and Related Party Notes Payable
Debt Instrument [Line Items]
Remaining in 2018	381,000
2,019	75,000
2,020	70,000
2,021	0
2,022	0
2023 and thereafter	25,000
Total	$ 551,000

Subordinated Debentures and S82

Subordinated Debentures and Subordinated Notes Payable - Junior Subordinated Deferrable Interest Debentures (Details) $ / shares in Units, $ in Thousands	6 Months Ended
	Mar. 31, 2018USD ($)trust$ / sharesshares	Sep. 30, 2017USD ($)
Debt Instrument [Line Items]
Maximum interest payment deferral period	5 years
Total subordinated debentures and subordinated notes payable	$ 108,385	$ 108,302
Junior Subordinated Debt
Debt Instrument [Line Items]
Total subordinated debentures and subordinated notes payable	73,557	73,511
Common shares held in other assets	$ 2,520	$ 2,520
Trust Preferred Securities Subject to Mandatory Redemption
Debt Instrument [Line Items]
Number of trusts | trust	7
Number of shares caused to be issued (in shares) | shares	73,400
Par value per shares issued (in dollars per share) | $ / shares	$ 1,000
Trust Preferred Securities Subject to Mandatory Redemption | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.48%
Trust Preferred Securities Subject to Mandatory Redemption | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.35%

Subordinated Debentures and S83

Subordinated Debentures and Subordinated Notes Payable - Subordinated Notes Payable (Details) - Subordinated Debt - USD ($)	12 Months Ended
	Sep. 30, 2015	Mar. 31, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Face amount of debt issued	$ 35,000,000
Stated interest rate (as a percent)	4.875%
Redemption price, percentage of principal (as a percent)	100.00%
Unamortized debt issuance costs		$ 172,000	$ 209,000
London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.15%

Subordinated Debentures and S84

Subordinated Debentures and Subordinated Notes Payable - Summary of Subordinated Debentures and Notes Payable (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2015
Debt Instrument [Line Items]
Total	$ 108,385	$ 108,302
Junior Subordinated Debt
Debt Instrument [Line Items]
Total subordinated debentures payable, amount outstanding	75,920	75,920
Total junior subordinated debentures payable, common shares held in other assets	2,520	2,520
Less: fair value adjustment	(2,363)	(2,409)
Total	73,557	73,511
Junior Subordinated Debt | GW Statutory Trust IV, variable rate of 2.85%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total subordinated debentures payable, amount outstanding	23,093	23,093
Total junior subordinated debentures payable, common shares held in other assets	$ 693	693
Basis spread on variable rate (as a percent)	2.85%
Junior Subordinated Debt | GW Statutory Trust VI, variable rate of 1.48%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total subordinated debentures payable, amount outstanding	$ 30,928	30,928
Total junior subordinated debentures payable, common shares held in other assets	$ 928	928
Basis spread on variable rate (as a percent)	1.48%
Junior Subordinated Debt | SSB Trust II, variable rate of 1.85%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total subordinated debentures payable, amount outstanding	$ 2,062	2,062
Total junior subordinated debentures payable, common shares held in other assets	$ 62	62
Basis spread on variable rate (as a percent)	1.85%
Junior Subordinated Debt | HF Capital Trust III, variable rate of 3.35%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total subordinated debentures payable, amount outstanding	$ 5,155	5,155
Total junior subordinated debentures payable, common shares held in other assets	$ 155	155
Basis spread on variable rate (as a percent)	3.35%
Junior Subordinated Debt | HF Capital Trust IV, variable rate of 3.10%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total subordinated debentures payable, amount outstanding	$ 7,217	7,217
Total junior subordinated debentures payable, common shares held in other assets	$ 217	217
Basis spread on variable rate (as a percent)	3.10%
Junior Subordinated Debt | HF Capital Trust V, variable rate of 1.83%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total subordinated debentures payable, amount outstanding	$ 5,310	5,310
Total junior subordinated debentures payable, common shares held in other assets	$ 310	310
Basis spread on variable rate (as a percent)	1.83%
Junior Subordinated Debt | HF Capital Trust VI, variable rate of 1.65%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total subordinated debentures payable, amount outstanding	$ 2,155	2,155
Total junior subordinated debentures payable, common shares held in other assets	$ 155	155
Basis spread on variable rate (as a percent)	1.65%
Subordinated Debt
Debt Instrument [Line Items]
Less: unamortized debt issuance costs	$ (172)	(209)
Total	34,828	34,791
Stated interest rate (as a percent)			4.875%
Subordinated Debt | Fixed to floating rate, 4.875% per annum
Debt Instrument [Line Items]
Total subordinated debentures payable, amount outstanding	$ 35,000	$ 35,000
Stated interest rate (as a percent)	4.875%

Income Taxes - (Narrative) (Det

Income Taxes - (Narrative) (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended			12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Mar. 31, 2018		Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Contingency [Line Items]
Federal tax rate		24.50%		35.00%	24.50%		35.00%
Provision for income taxes		$ 4,800			$ 9,800
Increase in provision for income taxes			$ 13,600
Tax Act - Stranded tax effects	[1]				$ 0
Great Western Bank
Income Tax Contingency [Line Items]
Effective income tax percentage		26.60%		34.10%	38.30%		32.20%
Effective income tax percentage, excluding nonrecurring deferred tax adjustment related to federal tax reform		26.60%			26.30%
Forecast
Income Tax Contingency [Line Items]
Federal tax rate								24.50%
Internal Revenue Service (IRS)
Income Tax Contingency [Line Items]
Income taxes receivable		$ 1,300			$ 1,300				$ 4,600
Accumulated Other Comprehensive Loss
Income Tax Contingency [Line Items]
Tax Act - Stranded tax effects		(2,400)			(2,353)	[1]
Retained Earnings
Income Tax Contingency [Line Items]
Tax Act - Stranded tax effects	[1]				$ 2,353
ASU 2018-02 | Accumulated Other Comprehensive Loss
Income Tax Contingency [Line Items]
Tax Act - Stranded tax effects		(2,400)
ASU 2018-02 | Retained Earnings
Income Tax Contingency [Line Items]
Tax Act - Stranded tax effects		$ 2,400
[1]	Reclassification due to adoption of ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. See Note 2, New Accounting Pronouncements and Note 15, Income Taxes, for additional information.

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Currently paid or payable
Federal	$ 11,791	$ 16,789	$ 20,752	$ 29,942
State	2,939	2,337	5,394	4,701
Current income tax expense (benefit)	14,730	19,126	26,146	34,643
Deferred tax expense
Federal	74	(1,044)	16,838	(566)
State	(85)	128	377	194
Total	(11)	(916)	17,215	(372)
Income tax expense	$ 14,719	$ 18,210	$ 43,361	$ 34,271

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense computed at the statutory rate	$ 13,552	$ 18,679	$ 27,748	$ 37,217
State income taxes, net of federal benefit	2,154	1,602	4,356	3,182
Tax exempt interest income	(1,415)	(1,996)	(2,786)	(4,034)
Impact of enacted federal income tax rate reduction	0	0	13,586	0
Other	428	(75)	457	(2,094)
Income tax expense	$ 14,719	$ 18,210	$ 43,361	$ 34,271

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Deferred tax assets:
Allowance for loan losses	$ 16,311	$ 23,730
Compensation	3,246	6,227
Securities available for sale	7,406	3,413
Other real estate owned	505	763
Core deposit intangible and other fair value adjustments	4,235	6,058
Excess tax basis of FDIC indemnification asset and clawback liability	3,574	4,563
Excess tax basis of loans acquired over carrying value	5,959	9,417
Other reserves	2,810	4,406
Other	4,988	6,922
Total deferred tax assets	49,034	65,499
Deferred tax liabilities:
Goodwill and other intangibles	(11,518)	(13,784)
Premises and equipment	(5,590)	(8,828)
Other	(297)	(487)
Total deferred tax liabilities	(17,405)	(23,099)
Net deferred tax assets	$ 31,629	$ 42,400

Employee Benefit Plans - Profit

Employee Benefit Plans - Profit Sharing Plan (Details) - Multiple employer 401(k) profit sharing plan $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Mar. 31, 2018USD ($)year	Mar. 31, 2017USD ($)
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, requisite service period			1 year
Defined contribution plan, minimum age requirement | year			21
Contributions by the Company | $	$ 1.2	$ 1.3	$ 3	$ 2.9

Employee Benefit Plans - Define

Employee Benefit Plans - Defined Benefit Plan (Details) - Pension Plan $ in Millions	Mar. 31, 2018USD ($)
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	$ 2.9
Pension liability	2.4
Accumulated benefit obligation	$ 5.4

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award, award vesting period			3 years
Share-based compensation expense	$ 1.4	$ 2	$ 2.9	$ 3.6
Tax benefit from compensation expense	0.4	$ 0.7	1	$ 1.4
Share-based compensation, compensation cost not yet recognized	$ 7.8		$ 7.8
Share-based compensation, compensation cost not yet recognized, recognition period			2 years 8 months 1 day
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of vested stock awards			$ 1.8

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Restricted Share and Performance-Based Stock Award Activity (Details) - $ / shares	6 Months Ended	12 Months Ended
	Mar. 31, 2018	Sep. 30, 2017
Restricted shares
Common Shares
Shares, beginning of fiscal year (in shares)	180,337	160,335
Granted (in shares)	89,003	90,363
Vested (in shares)	(81,999)	(68,293)
Forfeited (in shares)	(1,959)	(2,068)
Canceled (in shares)	0	0
Shares, end of period (in shares)	185,382	180,337
Vested, but not issuable at end of period (in shares)	39,514	29,287
Weighted-Average Grant Date Fair Value
Shares, beginning of fiscal year (in dollars per share)	$ 33.06	$ 26.89
Granted (in dollars per share)	41.07	39.35
Vested (in dollars per share)	32.12	26.97
Forfeited (in dollars per share)	40.30	30.91
Canceled (in dollars per share)	0	0
Shares, end of period (in dollars per share)	37.25	33.06
Vested, but not issuable at end of period (in dollars per share)	$ 32.90	$ 30.05
Performance shares
Common Shares
Shares, beginning of fiscal year (in shares)	133,604	236,185
Granted (in shares)	56,149	137,612
Vested (in shares)	0	(235,055)
Forfeited (in shares)	(2,178)	(5,138)
Canceled (in shares)	0	0
Shares, end of period (in shares)	187,575	133,604
Vested, but not issuable at end of period (in shares)	5,612	5,612
Weighted-Average Grant Date Fair Value
Shares, beginning of fiscal year (in dollars per share)	$ 33.39	$ 20.28
Granted (in dollars per share)	28.92	39.43
Vested (in dollars per share)	0	18
Forfeited (in dollars per share)	39.71	19.80
Canceled (in dollars per share)	0	0
Shares, end of period (in dollars per share)	35.63	33.39
Vested, but not issuable at end of period (in dollars per share)	$ 18	$ 18

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value Measurements of Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	$ 1,307,598	$ 1,367,960
Fair value loans	920,965	1,016,576
U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	177,419	228,603
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,060,277	1,065,737
States and political subdivision securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	68,900	72,586
Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,307,598	1,367,960
Derivatives-assets	2,832	0
Derivatives-liabilities	1,118	17,155
Fair value loans	920,965	1,016,576
Fair value, measurements, recurring | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	177,419	228,603
Fair value, measurements, recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,060,277	1,065,737
Fair value, measurements, recurring | States and political subdivision securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	68,900	72,586
Fair value, measurements, recurring | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,002	1,034
Fair value, measurements, recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	177,419	228,603
Derivatives-assets	0	0
Derivatives-liabilities	0	0
Fair value loans	0	0
Fair value, measurements, recurring | Level 1 | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	177,419	228,603
Fair value, measurements, recurring | Level 1 | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Fair value, measurements, recurring | Level 1 | States and political subdivision securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Fair value, measurements, recurring | Level 1 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,129,214	1,138,288
Derivatives-assets	2,832	0
Derivatives-liabilities	1,118	17,155
Fair value loans	920,965	1,016,576
Fair value, measurements, recurring | Level 2 | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Fair value, measurements, recurring | Level 2 | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,060,277	1,065,737
Fair value, measurements, recurring | Level 2 | States and political subdivision securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	67,935	71,517
Fair value, measurements, recurring | Level 2 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,002	1,034
Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	965	1,069
Derivatives-assets	0	0
Derivatives-liabilities	0	0
Fair value loans	0	0
Fair value, measurements, recurring | Level 3 | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Fair value, measurements, recurring | Level 3 | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Fair value, measurements, recurring | Level 3 | States and political subdivision securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	965	1,069
Fair value, measurements, recurring | Level 3 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	$ 0	$ 0

Fair Value Measurements - Sch94

Fair Value Measurements - Schedule of Changes in Level 3 Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 965	$ 1,224	$ 1,069	$ 1,315
Principal paydown	0	0	(104)	(91)
Balance, end of period	$ 965	$ 1,224	$ 965	$ 1,224

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Mortgage Loans Held-For-Sale, Fair Value Measurement (Details) - Fair value, measurements, nonrecurring - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other repossessed property	$ 7,679	$ 7,728
Impaired loans	198,609	185,388
Loans held for sale, at lower of cost or fair value	2,429	7,456
Loan servicing rights	3,586	4,074
Property held for sale	1,109	5,147
Level 1
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other repossessed property	0	0
Impaired loans	0	0
Loans held for sale, at lower of cost or fair value	0	0
Loan servicing rights	0	0
Property held for sale	0	0
Level 2
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other repossessed property	0	0
Impaired loans	0	0
Loans held for sale, at lower of cost or fair value	2,429	7,456
Loan servicing rights	0	0
Property held for sale	0	0
Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other repossessed property	7,679	7,728
Impaired loans	198,609	185,388
Loans held for sale, at lower of cost or fair value	0	0
Loan servicing rights	3,586	4,074
Property held for sale	$ 1,109	$ 5,147

Fair Value Measurements - Sum96

Fair Value Measurements - Summary of Valuation Techniques and Significant Unobservable Inputs Used to Measure Level 3 Fair Value Measurements (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Sep. 30, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Property held for sale	$ 1,109	$ 5,147
Fair value, measurements, nonrecurring
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other real estate owned	7,679	7,728
Impaired loans	198,609	185,388
Loan servicing rights	3,586	4,074
Fair value, measurements, nonrecurring | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other real estate owned	7,679	7,728
Impaired loans	198,609	185,388
Loan servicing rights	3,586	$ 4,074
Property held for sale	$ 1,109
Fair value, measurements, nonrecurring | Level 3 | Loan servicing rights | Discounted cash flows | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Constant prepayment rate (as a percent)	7.90%
Discount rate (as a percent)	10.00%
Fair value, measurements, nonrecurring | Level 3 | Loan servicing rights | Discounted cash flows | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Constant prepayment rate (as a percent)	20.50%
Discount rate (as a percent)	15.00%
Fair value, measurements, nonrecurring | Level 3 | Loan servicing rights | Discounted cash flows | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Constant prepayment rate (as a percent)	10.40%
Discount rate (as a percent)	11.80%

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details)	6 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Derivative, remaining maturity (or less)	180 days

Fair Value Measurements - Sch98

Fair Value Measurements - Schedule of Fair Values for Balance Sheet Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Level 1 | Carrying Amount
Assets
Cash and cash equivalents	$ 371,749	$ 360,396
Level 1 | Fair Value
Assets
Cash and cash equivalents	371,749	360,396
Level 3 | Carrying Amount
Assets
Loans, net excluding fair valued loans and loans held for sale	8,349,772	7,881,018
Level 3 | Fair Value
Assets
Loans, net excluding fair valued loans and loans held for sale	8,238,751	7,798,134
Level 2 | Carrying Amount
Assets
Accrued interest receivable	49,353	53,176
Cash surrender value of life insurance policies	30,032	29,619
FHLB stock	33,720	37,551
Liabilities
Deposits	9,386,967	8,977,613
FHLB advances and other borrowings	551,003	643,214
Securities sold under repurchase agreements	103,291	132,636
Accrued interest payable	6,165	4,405
Subordinated debentures and subordinated notes payable	108,385	108,302
Level 2 | Fair Value
Assets
Accrued interest receivable	49,353	53,176
Cash surrender value of life insurance policies	30,032	29,619
FHLB stock	33,720	37,551
Liabilities
Deposits	9,384,577	8,978,926
FHLB advances and other borrowings	477,292	645,421
Securities sold under repurchase agreements	103,291	132,636
Accrued interest payable	6,165	4,405
Subordinated debentures and subordinated notes payable	$ 107,826	$ 108,293

Earnings per Share - Schedule o

Earnings per Share - Schedule of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 40,532	$ 35,162	$ 69,762	$ 72,065
Weighted average common shares outstanding (in shares)	58,941,315	58,788,802	58,921,972	58,769,662
Dilutive effect of stock based compensation (in shares)	204,802	284,867	194,951	263,125
Weighted average common shares outstanding for diluted earnings per share calculation (in shares)	59,146,117	59,073,669	59,116,923	59,032,787
Basic earnings per share (in dollars per share)	$ 0.69	$ 0.60	$ 1.18	$ 1.23
Diluted earnings per share (in dollars per share)	$ 0.69	$ 0.60	$ 1.18	$ 1.22

Earnings per Share - Narrative

Earnings per Share - Narrative (Details) - shares	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Performance shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share (in shares)	0	50,076
Stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share (in shares)	0	53,126