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Fair Value Measurements - Fair Value by Balance Sheet Grouping (Details) - USD ($) $ in Thousands | Dec. 31, 2018 | Sep. 30, 2018
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities |  | $ 1,314,957
Held-to-maturity securities | $ 1,537,496 | 1,548,770
FHLB and FRB stock | 135,590 | 127,190
Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 1,451,340 | 1,314,957
Held-to-maturity securities | 1,586,815 | 1,625,420
Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 1,451,340 | 1,314,957
Held-to-maturity securities | 1,537,496 | 1,548,770
Level 1 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Cash and cash equivalents | 283,375 | 268,650
Level 1 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Cash and cash equivalents | 283,375 | 268,650
Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
FHLB and FRB stock | 135,590 | 127,190
Time deposit accounts | 4,817,346 | 4,804,803
FHLB advances | 2,540,000 | 2,330,000
Level 2 | Carrying Amount | Interest rate contracts |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 3,341 | 12,731
Other liabilities | 3,341 | 12,731
Level 2 | Carrying Amount | Commercial loan hedges |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 1,506 | 3,857
Level 2 | Carrying Amount | Borrowings cash flow hedges |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 11,751 | 22,250
Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
FHLB and FRB stock | 135,590 | 127,190
Time deposit accounts | 4,822,783 | 4,779,040
FHLB advances | 2,537,375 | 2,316,964
Level 2 | Estimated Fair Value | Interest rate contracts |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 3,341 | 12,731
Other liabilities | 3,341 | 12,731
Level 2 | Estimated Fair Value | Commercial loan hedges |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 1,506 | 3,857
Level 2 | Estimated Fair Value | Borrowings cash flow hedges |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Other assets | 11,751 | 22,250
Level 3 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Loans receivable | 11,700,239 | 11,477,081
Level 3 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Loans receivable | 12,020,772 | 11,556,326
Equity securities | Level 1 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities |  | 488
Equity securities | Level 1 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities |  | 488
U.S. government and agency securities | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 200,704 | 207,293
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 | 200,704 | 207,293
Municipal bonds | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 23,058 | 22,978
Municipal bonds | Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 23,058 | 22,978
Corporate debt securities | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 222,541 | 184,695
Corporate debt securities | Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 222,541 | 184,695
Agency pass-through certificates |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Held-to-maturity securities | 1,522,571 | 1,533,742
Agency pass-through certificates | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 1,005,037 | 896,041
Held-to-maturity securities | 1,571,815 | 1,610,420
Agency pass-through certificates | Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 1,005,037 | 896,041
Held-to-maturity securities | 1,522,571 | 1,533,742
Commercial MBS |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Held-to-maturity securities | 14,925 | 15,028
Commercial MBS | Level 2 | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 0 | 3,462
Held-to-maturity securities | 15,000 | 15,000
Commercial MBS | Level 2 | Estimated Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Available-for-sale securities | 0 | 3,462
Held-to-maturity securities | $ 14,925 | $ 15,028

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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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