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Loans Held for Investment - Schedule of Allowance for Credit Losses for Loans Held for Investment (Details) |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Feb. 01, 2022 USD ($) | Sep. 30, 2022 USD ($) Investments | Sep. 30, 2021 USD ($) | Sep. 30, 2022 USD ($) Investments | Sep. 30, 2021 USD ($) | Dec. 31, 2021 USD ($) Investments
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | $ 220,400,000 | $ 135,500,000 | $ 122,300,000 | $ 144,300,000 |
Provision charged to operating expense |  | 8,400,000 | 0 | 68,000,000.0 | (5,100,000) |
Loans Charged-Off |  | (16,200,000) | (2,100,000) | (39,800,000) | (11,800,000) |
Ending balance |  | 213,000,000.0 | 135,100,000 | 213,000,000.0 | 135,100,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 59,500,000 |  |
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal) |  | 4,600,000 | 200,000 | 60,200,000 | (4,600,000) |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 4,200,000 | 1,500,000 | 10,800,000 | 7,200,000 |
Interest Receivable |  | 106,400,000 |  | 106,400,000 |  | $ 47,400,000
Debt Securities, Available-for-sale, Realized Loss |  | 46,300,000 | 0 | 46,400,000 | 0 |
Debt Securities, Held-To-Maturity, After Allowance For Credit Loss, Transfer, Amount | $ 10,900,000 |  |  |  |  |
Debt Securities, Available-For-Sale, Amortized Cost, after Allowance for Credit Loss, Transfer, Amount | 485,900,000 |  |  |  |  |
Debt Securities, Available-For-Sale, after Allowance for Credit Loss, Transfer, Amount | 463,600,000 |  |  |  |  |
Debt Securities, Held-to-maturity, Transfer to Trading, Unrealized Gain (Loss) | 0 |  |  |  |  |
Allowance for Credit Losses |  | $ 0 |  | $ 0 |  | $ 0
Investment securities in an unrealized loss position (securities) | Investments |  | 1,239 |  | 1,239 |  | 285
Debt Securities, Available-for-sale, Realized Gain |  | $ 0 | 0 | $ 0 | 0 |
Securities Sold under Agreements to Repurchase, Fair Value of Collateral |  | 4,836,700,000 |  | 4,836,700,000 |  | $ 2,617,800,000
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure |  | 4,265,100,000 |  | 4,265,100,000 |  | 2,610,800,000
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Transfer, Amount | 10,700,000 |  |  |  |  |
Callable Within One Year |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Amortized cost of investment securities callable after one year but within five years |  | 777,700,000 |  | 777,700,000 |  |
Fair value of investment securities callable after one year but within five years |  | 706,200,000 |  | 706,200,000 |  |
Callable structured notes amortized costs |  | 0 |  | 0 |  |
Great Western Bank |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal) |  | 68,300,000 |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Debt Securities, Available-For-Sale | 2,356,900,000 |  |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Debt Securities, Held-To-Maturity | $ 342,100,000 |  |  |  |  |
Debt Securities |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Interest Receivable |  | 34,300,000 |  | 34,300,000 |  | $ 16,600,000
Commercial Real Estate Non Owner Occupied Loans [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 29,500,000 | 22,900,000 | 17,300,000 | 25,500,000 |
Provision charged to operating expense |  | (5,500,000) | 1,100,000 | (7,600,000) | (1,600,000) |
Loans Charged-Off |  | (100,000) | 0 | (3,000,000.0) | 0 |
Ending balance |  | 23,900,000 | 24,000,000.0 | 23,900,000 | 24,000,000.0 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 17,200,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 0 | 0 | 0 | 100,000 |
Agricultural Financing Receivable [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 6,500,000 | 400,000 | 300,000 | 700,000 |
Provision charged to operating expense |  | (2,500,000) | 0 | 3,300,000 | (100,000) |
Loans Charged-Off |  | 0 | 0 | (5,400,000) | (200,000) |
Ending balance |  | 4,000,000.0 | 400,000 | 4,000,000.0 | 400,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 4,500,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 0 | 0 | 1,300,000 | 0 |
Commercial and Floor Plans [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 54,100,000 | 29,000,000.0 | 27,100,000 | 34,200,000 |
Provision charged to operating expense |  | (2,200,000) | 300,000 | 18,100,000 | (4,900,000) |
Loans Charged-Off |  | (500,000) | (100,000) | (5,800,000) | (2,200,000) |
Ending balance |  | 52,400,000 | 29,400,000 | 52,400,000 | 29,400,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 11,200,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 1,000,000.0 | 200,000 | 1,800,000 | 2,300,000 |
Commercial Real Estate Owner Occupied [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 26,600,000 | 16,600,000 | 13,300,000 | 18,300,000 |
Provision charged to operating expense |  | (3,700,000) | (600,000) | 2,300,000 | 0 |
Loans Charged-Off |  | 0 | 0 | (2,200,000) | (2,300,000) |
Ending balance |  | 24,700,000 | 16,000,000.0 | 24,700,000 | 16,000,000.0 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 9,500,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 1,800,000 | 0 | 1,800,000 | 0 |
Commercial Real Estate Multi-family [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 33,400,000 | 11,600,000 | 13,300,000 | 11,000,000.0 |
Provision charged to operating expense |  | (2,600,000) | 200,000 | 5,900,000 | 800,000 |
Loans Charged-Off |  | (5,700,000) | 0 | (5,700,000) | 0 |
Ending balance |  | 25,100,000 | 11,800,000 | 25,100,000 | 11,800,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 10,900,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 0 | 0 | 700,000 | 0 |
Commercial real estate |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 89,500,000 | 51,100,000 | 43,900,000 | 54,800,000 |
Provision charged to operating expense |  | (11,800,000) | 700,000 | 600,000 | (800,000) |
Loans Charged-Off |  | (5,800,000) | 0 | (10,900,000) | (2,300,000) |
Ending balance |  | 73,700,000 | 51,800,000 | 73,700,000 | 51,800,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 37,600,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 1,800,000 | 0 | 2,500,000 | 100,000 |
Land Acquisition And Development Construction Financing Receivable [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 800,000 | 1,000,000.0 | 500,000 | 1,300,000 |
Provision charged to operating expense |  | (200,000) | (200,000) | (800,000) | (800,000) |
Loans Charged-Off |  | 0 | 0 | (2,700,000) | (100,000) |
Ending balance |  | 700,000 | 900,000 | 700,000 | 900,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 3,400,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 100,000 | 100,000 | 300,000 | 500,000 |
Residential construction |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 3,400,000 | 1,500,000 | 2,400,000 | 1,600,000 |
Provision charged to operating expense |  | (300,000) | 300,000 | 700,000 | 300,000 |
Loans Charged-Off |  | 0 | 0 | 0 | (100,000) |
Ending balance |  | 3,100,000 | 1,800,000 | 3,100,000 | 1,800,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 0 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 0 | 0 | 0 | 0 |
Commercial construction |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 14,900,000 | 8,000,000.0 | 6,000,000.0 | 7,300,000 |
Provision charged to operating expense |  | 16,400,000 | (1,300,000) | 25,100,000 | (600,000) |
Loans Charged-Off |  | (6,600,000) | 0 | (6,600,000) | (100,000) |
Ending balance |  | 24,700,000 | 6,700,000 | 24,700,000 | 6,700,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 200,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 0 | 0 | 0 | 100,000 |
Construction Loans [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 19,100,000 | 10,500,000 | 8,900,000 | 10,200,000 |
Provision charged to operating expense |  | 15,900,000 | (1,200,000) | 25,000,000.0 | (1,100,000) |
Loans Charged-Off |  | (6,600,000) | 0 | (9,300,000) | (300,000) |
Ending balance |  | 28,500,000 | 9,400,000 | 28,500,000 | 9,400,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 3,600,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 100,000 | 100,000 | 300,000 | 600,000 |
Residential Real Estate 1-4 Family [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 18,200,000 | 13,400,000 | 13,400,000 | 11,400,000 |
Provision charged to operating expense |  | 900,000 | (200,000) | 5,400,000 | 1,800,000 |
Loans Charged-Off |  | 0 | 0 | (100,000) | 0 |
Ending balance |  | 19,100,000 | 13,200,000 | 19,100,000 | 13,200,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 100,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 0 | 0 | 300,000 | 0 |
Home Equity Line of Credit [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 1,500,000 | 1,400,000 | 1,200,000 | 1,400,000 |
Provision charged to operating expense |  | 100,000 | (100,000) | 100,000 | (200,000) |
Loans Charged-Off |  | (100,000) | 0 | (100,000) | (100,000) |
Ending balance |  | 1,600,000 | 1,400,000 | 1,600,000 | 1,400,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 0 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 100,000 | 100,000 | 400,000 | 300,000 |
Residential Real Estate [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 19,700,000 | 14,800,000 | 14,600,000 | 12,800,000 |
Provision charged to operating expense |  | 1,000,000.0 | (300,000) | 5,500,000 | 1,600,000 |
Loans Charged-Off |  | (100,000) | 0 | (200,000) | (100,000) |
Ending balance |  | 20,700,000 | 14,600,000 | 20,700,000 | 14,600,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 100,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 100,000 | 100,000 | 700,000 | 300,000 |
Agricultural Real Estate Financing Receivable [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 5,400,000 | 3,000,000.0 | 1,900,000 | 2,700,000 |
Provision charged to operating expense |  | 400,000 | 100,000 | 1,700,000 | 400,000 |
Loans Charged-Off |  | 0 | 0 | (200,000) | 0 |
Ending balance |  | 5,800,000 | 3,100,000 | 5,800,000 | 3,100,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 2,300,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 0 | 0 | 100,000 | 0 |
Real Estate Financing Receivable [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 133,700,000 | 79,400,000 | 69,300,000 | 80,500,000 |
Provision charged to operating expense |  | 5,500,000 | (700,000) | 32,800,000 | 100,000 |
Loans Charged-Off |  | (12,500,000) | 0 | (20,600,000) | (2,700,000) |
Ending balance |  | 128,700,000 | 78,900,000 | 128,700,000 | 78,900,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 43,600,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 2,000,000.0 | 200,000 | 3,600,000 | 1,000,000.0 |
Consumer Indirect Financing Receivable [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 13,100,000 | 15,800,000 | 14,300,000 | 16,700,000 |
Provision charged to operating expense |  | 1,600,000 | (100,000) | 900,000 | (300,000) |
Loans Charged-Off |  | (1,200,000) | (800,000) | (2,900,000) | (2,900,000) |
Ending balance |  | 14,100,000 | 15,400,000 | 14,100,000 | 15,400,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 0 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 600,000 | 500,000 | 1,800,000 | 1,900,000 |
Direct consumer |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 5,000,000.0 | 4,600,000 | 4,600,000 | 4,600,000 |
Provision charged to operating expense |  | 1,300,000 | 500,000 | 1,700,000 | 1,200,000 |
Loans Charged-Off |  | (1,400,000) | (800,000) | (2,800,000) | (2,000,000.0) |
Ending balance |  | 5,300,000 | 4,700,000 | 5,300,000 | 4,700,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 0 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 400,000 | 400,000 | 1,800,000 | 900,000 |
Credit Card Receivable [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 2,200,000 | 1,600,000 | 2,200,000 | 2,600,000 |
Provision charged to operating expense |  | 300,000 | 400,000 | 1,600,000 | 0 |
Loans Charged-Off |  | (300,000) | (400,000) | (1,800,000) | (1,400,000) |
Ending balance |  | 2,400,000 | 1,800,000 | 2,400,000 | 1,800,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 0 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 200,000 | 200,000 | 400,000 | 600,000 |
Consumer |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 20,300,000 | 22,000,000.0 | 21,100,000 | 23,900,000 |
Provision charged to operating expense |  | 3,200,000 | 800,000 | 4,200,000 | 900,000 |
Loans Charged-Off |  | (2,900,000) | (2,000,000.0) | (7,500,000) | (6,300,000) |
Ending balance |  | 21,800,000 | 21,900,000 | 21,800,000 | 21,900,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 0 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 1,200,000 | 1,100,000 | 4,000,000.0 | 3,400,000 |
Commercial Purpose secured by 1-4 Family [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 5,500,000 | 4,400,000 | 4,400,000 | 4,700,000 |
Provision charged to operating expense |  | 400,000 | (200,000) | 1,200,000 | (800,000) |
Loans Charged-Off |  | 0 | 0 | 0 | (100,000) |
Ending balance |  | 5,900,000 | 4,200,000 | 5,900,000 | 4,200,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 200,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 0 | 0 | 100,000 | 400,000 |
Commercial Borrower [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 300,000 | 300,000 | 100,000 | 300,000 |
Provision charged to operating expense |  | 200,000 | 0 | 600,000 | 200,000 |
Loans Charged-Off |  | (300,000) | 0 | (500,000) | (300,000) |
Ending balance |  | 200,000 | 300,000 | 200,000 | 300,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 0 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | 0 | 0 | 0 | 100,000 |
Commercial Portfolio Segment [Member] |  |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss [Roll Forward] |  |  |  |  |  |
Beginning balance |  | 59,900,000 | 33,700,000 | 31,600,000 | 39,200,000 |
Provision charged to operating expense |  | (1,600,000) | 100,000 | 19,900,000 | (5,500,000) |
Loans Charged-Off |  | (800,000) | (100,000) | (6,300,000) | (2,600,000) |
Ending balance |  | 58,500,000 | 33,900,000 | 58,500,000 | 33,900,000 |
Provisional ACL Recorded for PCD loans |  | 0 |  | 11,400,000 |  |
Financing Receivable, Allowance for Credit Loss, Recovery |  | $ 1,000,000.0 | $ 200,000 | $ 1,900,000 | $ 2,800,000 |

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