Loans - Troubled Debt Restructurings on Accruing and Nonaccrual Financing Receivables (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2016 USD ($) contract	Sep. 30, 2015 USD ($) contract	Sep. 30, 2014 USD ($) contract
Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 46,568	$ 60,371
Financing receivable, modifications, number of contracts | contract	38	28	61
Financing receivable, modifications, pre-modification recorded investment	$ 46,393	$ 46,783	$ 13,612
Financing receivable, modifications, post-modification recorded investment	$ 46,393	$ 46,783	$ 13,612
Change in recorded investment due to principal paydown at time of modification, number of contracts | contract	0	0	0
Change in recorded investment due to principal paydown at time of modification, pre-modification	$ 0	$ 0	$ 0
Change in recorded investment due to principal paydown at time of modification, post-modification	$ 0	$ 0	$ 0
Change in recorded investment due to chargeoffs at time of modification, number of contracts | contract	0	0	0
Change in recorded investment due to chargeoffs at time of modification, pre-modification	$ 0	$ 0	$ 0
Change in recorded investment due to chargeoffs at time of modification, post-modification	0	0	$ 0
Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 36,778	$ 13,966
Financing receivable, modifications, number of contracts | contract	12	22	70
Financing receivable, modifications, pre-modification recorded investment	$ 2,150	$ 2,681	$ 8,977
Financing receivable, modifications, post-modification recorded investment	$ 2,103	$ 2,536	$ 8,977
Change in recorded investment due to principal paydown at time of modification, number of contracts | contract	0	0	0
Change in recorded investment due to principal paydown at time of modification, pre-modification	$ 0	$ 0	$ 0
Change in recorded investment due to principal paydown at time of modification, post-modification	$ 0	$ 0	$ 0
Change in recorded investment due to chargeoffs at time of modification, number of contracts | contract	7	5	0
Change in recorded investment due to chargeoffs at time of modification, pre-modification	$ 47	$ 145	$ 0
Change in recorded investment due to chargeoffs at time of modification, post-modification	0	0	$ 0
Residential real estate | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 370	$ 452
Financing receivable, modifications, number of contracts | contract	1	4	23
Financing receivable, modifications, pre-modification recorded investment	$ 42	$ 85	$ 1,067
Financing receivable, modifications, post-modification recorded investment	$ 42	$ 85	$ 1,067
Residential real estate | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	1	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 13	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 13	$ 0
Residential real estate | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	1	2	6
Financing receivable, modifications, pre-modification recorded investment	$ 42	$ 53	$ 206
Financing receivable, modifications, post-modification recorded investment	$ 42	$ 53	$ 206
Residential real estate | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	6
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 474
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 474
Residential real estate | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	1	9
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 19	$ 338
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 19	$ 338
Residential real estate | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	2
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 49
Financing receivable, modifications, post-modification recorded investment	0	0	$ 49
Residential real estate | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 937	$ 1,547
Financing receivable, modifications, number of contracts | contract	3	7	42
Financing receivable, modifications, pre-modification recorded investment	$ 254	$ 318	$ 1,389
Financing receivable, modifications, post-modification recorded investment	$ 253	$ 302	$ 1,389
Residential real estate | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	1	5
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 67	$ 119
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 67	$ 119
Residential real estate | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	3	13
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 169	$ 351
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 169	$ 351
Residential real estate | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	3	1	6
Financing receivable, modifications, pre-modification recorded investment	$ 254	$ 19	$ 219
Financing receivable, modifications, post-modification recorded investment	$ 253	$ 19	$ 219
Residential real estate | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	1	7
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 39	$ 275
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 39	$ 275
Residential real estate | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	1	11
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 24	$ 425
Financing receivable, modifications, post-modification recorded investment	0	8	$ 425
Commercial real estate | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 18,250	$ 30,917
Financing receivable, modifications, number of contracts | contract	5	7	5
Financing receivable, modifications, pre-modification recorded investment	$ 8,611	$ 22,709	$ 3,020
Financing receivable, modifications, post-modification recorded investment	$ 8,611	$ 22,709	$ 3,020
Commercial real estate | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Commercial real estate | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	2	0	3
Financing receivable, modifications, pre-modification recorded investment	$ 1,897	$ 0	$ 109
Financing receivable, modifications, post-modification recorded investment	$ 1,897	$ 0	$ 109
Commercial real estate | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	6	2
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 22,232	$ 2,911
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 22,232	$ 2,911
Commercial real estate | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	1	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 477	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 477	$ 0
Commercial real estate | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	3	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 6,714	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	6,714	0	$ 0
Commercial real estate | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 2,356	$ 4,725
Financing receivable, modifications, number of contracts | contract	0	4	6
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 1,822	$ 5,736
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 1,822	$ 5,736
Commercial real estate | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	3
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 1,618
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 1,618
Commercial real estate | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	2	2
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 740	$ 4,031
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 740	$ 4,031
Commercial real estate | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	2	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 1,082	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 1,082	$ 0
Commercial real estate | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Commercial real estate | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	1
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 87
Financing receivable, modifications, post-modification recorded investment	0	0	$ 87
Commercial non real estate | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 8,102	$ 8,928
Financing receivable, modifications, number of contracts | contract	12	6	22
Financing receivable, modifications, pre-modification recorded investment	$ 9,617	$ 4,005	$ 6,721
Financing receivable, modifications, post-modification recorded investment	$ 9,617	$ 4,005	$ 6,721
Commercial non real estate | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	1	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 49	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 49	$ 0	$ 0
Commercial non real estate | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	5	2	7
Financing receivable, modifications, pre-modification recorded investment	$ 120	$ 2,296	$ 2,183
Financing receivable, modifications, post-modification recorded investment	$ 120	$ 2,296	$ 2,183
Commercial non real estate | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	2	4	10
Financing receivable, modifications, pre-modification recorded investment	$ 948	$ 1,709	$ 3,593
Financing receivable, modifications, post-modification recorded investment	$ 948	$ 1,709	$ 3,593
Commercial non real estate | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Commercial non real estate | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	4	0	5
Financing receivable, modifications, pre-modification recorded investment	$ 8,500	$ 0	$ 945
Financing receivable, modifications, post-modification recorded investment	8,500	0	$ 945
Commercial non real estate | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 4,789	$ 833
Financing receivable, modifications, number of contracts | contract	2	8	12
Financing receivable, modifications, pre-modification recorded investment	$ 760	$ 311	$ 484
Financing receivable, modifications, post-modification recorded investment	$ 760	$ 183	$ 484
Commercial non real estate | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	1	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 32	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Commercial non real estate | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	5	10
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 257	$ 438
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 180	$ 438
Commercial non real estate | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	2	2	1
Financing receivable, modifications, pre-modification recorded investment	$ 760	$ 22	$ 36
Financing receivable, modifications, post-modification recorded investment	$ 760	$ 3	$ 36
Commercial non real estate | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	1
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 10
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 10
Commercial non real estate | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	0	0	$ 0
Agriculture | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 19,823	$ 20,041
Financing receivable, modifications, number of contracts | contract	20	9	5
Financing receivable, modifications, pre-modification recorded investment	$ 28,123	$ 19,961	$ 2,755
Financing receivable, modifications, post-modification recorded investment	$ 28,123	$ 19,961	$ 2,755
Agriculture | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Agriculture | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	16	2	5
Financing receivable, modifications, pre-modification recorded investment	$ 27,134	$ 1,410	$ 2,755
Financing receivable, modifications, post-modification recorded investment	$ 27,134	$ 1,410	$ 2,755
Agriculture | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	4	7	0
Financing receivable, modifications, pre-modification recorded investment	$ 989	$ 18,551	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 989	$ 18,551	$ 0
Agriculture | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Agriculture | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	0	0	$ 0
Agriculture | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 28,688	$ 6,857
Financing receivable, modifications, number of contracts | contract	6	1	5
Financing receivable, modifications, pre-modification recorded investment	$ 1,128	$ 229	$ 1,342
Financing receivable, modifications, post-modification recorded investment	$ 1,082	$ 229	$ 1,342
Agriculture | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Agriculture | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	1	0	3
Financing receivable, modifications, pre-modification recorded investment	$ 101	$ 0	$ 831
Financing receivable, modifications, post-modification recorded investment	$ 100	$ 0	$ 831
Agriculture | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	4	1	0
Financing receivable, modifications, pre-modification recorded investment	$ 932	$ 229	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 887	$ 229	$ 0
Agriculture | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Agriculture | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	1	0	2
Financing receivable, modifications, pre-modification recorded investment	$ 95	$ 0	$ 511
Financing receivable, modifications, post-modification recorded investment	95	0	$ 511
Consumer | Accruing
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 23	$ 33
Financing receivable, modifications, number of contracts | contract	0	2	6
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 23	$ 49
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 23	$ 49
Consumer | Accruing | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Consumer | Accruing | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Consumer | Accruing | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	1	4
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 17	$ 21
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 17	$ 21
Consumer | Accruing | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	1	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 6	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 6	$ 0
Consumer | Accruing | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	2
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 28
Financing receivable, modifications, post-modification recorded investment	0	0	$ 28
Consumer | Nonaccrual
Financing Receivable, Modifications [Line Items]
Recorded value of TDR balance	$ 8	$ 4
Financing receivable, modifications, number of contracts | contract	1	2	5
Financing receivable, modifications, pre-modification recorded investment	$ 8	$ 1	$ 26
Financing receivable, modifications, post-modification recorded investment	$ 8	$ 0	$ 26
Consumer | Nonaccrual | Rate modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Consumer | Nonaccrual | Term extension
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	2	2
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 1	$ 15
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 15
Consumer | Nonaccrual | Payment modification
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	1
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 2
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 2
Consumer | Nonaccrual | Bankruptcy
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	1	0	0
Financing receivable, modifications, pre-modification recorded investment	$ 8	$ 0	$ 0
Financing receivable, modifications, post-modification recorded investment	$ 8	$ 0	$ 0
Consumer | Nonaccrual | Other
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts | contract	0	0	2
Financing receivable, modifications, pre-modification recorded investment	$ 0	$ 0	$ 9
Financing receivable, modifications, post-modification recorded investment	$ 0	$ 0	$ 9