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Fair Value Measurements - Fair Value by Balance Sheet Grouping (Details) - USD ($) $ in Thousands | Jun. 30, 2018 | Sep. 30, 2017
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | $ 1,255,401 | $ 1,266,209
Held-to-maturity securities | 1,610,034 | 1,635,913
FHLB and FRB stock | 128,790 | 122,990
Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 1,255,401 | 1,266,209
Held-to-maturity securities | 1,670,450 | 1,646,856
Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 1,255,401 | 1,266,209
Held-to-maturity securities | 1,610,034 | 1,635,913
Level 1 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Cash and cash equivalents | 345,919 | 313,070
Level 1 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Cash and cash equivalents | 345,919 | 313,070
Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
FHLB and FRB stock | 128,790 | 122,990
Customer accounts | 11,287,473 | 10,835,008
FHLB advances | 2,370,000 | 2,225,000
Level 2 | Carrying Amount | Interest rate contracts |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 10,141 | 1,139
Other liabilities | 10,141 | 1,139
Level 2 | Carrying Amount | Commercial loan hedges |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 3,005 | 0
Other liabilities | 0 | 174
Level 2 | Carrying Amount | Borrowings hedges |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 19,193 | 0
Other liabilities | 0 | 1,693
Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
FHLB and FRB stock | 128,790 | 122,990
Customer accounts | 10,924,562 | 10,411,686
FHLB advances | 2,365,478 | 2,266,791
Level 2 | Estimated Fair Value | Interest rate contracts |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 10,141 | 1,139
Other liabilities | 10,141 | 1,139
Level 2 | Estimated Fair Value | Commercial loan hedges |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 3,005 | 0
Other liabilities | 0 | 174
Level 2 | Estimated Fair Value | Borrowings hedges |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 19,193 | 0
Other liabilities | 0 | 1,693
Level 3 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Loans receivable | 11,325,971 | 10,882,622
FDIC indemnification asset | 0 | 8,968
Level 3 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Loans receivable | 11,492,022 | 11,247,586
FDIC indemnification asset | 0 | 8,564
Equity securities | Level 1 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 491 | 522
Equity securities | Level 1 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 491 | 522
U.S. government and agency securities | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 216,009 | 211,077
U.S. government and agency securities | Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 216,009 | 211,077
Municipal bonds | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 22,755 | 26,624
Municipal bonds | Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 22,755 | 26,624
Corporate debt securities | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 184,232 | 185,298
Corporate debt securities | Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 184,232 | 185,298
Agency pass-through certificates |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Held-to-maturity securities | 1,595,034 | 1,635,913
Agency pass-through certificates | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 828,449 | 834,297
Held-to-maturity securities | 1,655,450 | 1,646,856
Agency pass-through certificates | Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 828,449 | 834,297
Held-to-maturity securities | 1,595,034 | 1,635,913
Commercial MBS |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Held-to-maturity securities | 15,000 |
Commercial MBS | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 3,465 | 8,391
Held-to-maturity securities | 15,000 | 0
Commercial MBS | Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 3,465 | 8,391
Held-to-maturity securities | $ 15,000 | $ 0

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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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- Definition Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809 + Details
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