| Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] |
Assets and liabilities measured at fair value on a recurring and nonrecurring basis were as follows at the dates indicated: | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fair Value Measurements at Reporting Date Using | | Balance | | Quoted Prices
in Active
Markets for
Identical
Assets
(Level 1) | | Significant
Other
Observable
Inputs
(Level 2) | | Significant
Unobservable
Inputs
(Level 3) | | | September 30, 2023 | | | (Dollars in thousands) | | Recurring fair value measurements | | | | | | | | | Assets | | | | | | | | | Trading securities | $ | 4,476 | | | $ | 4,476 | | | $ | — | | | $ | — | | | Equity securities | 21,475 | | | 21,475 | | | — | | | — | | | Securities available for sale | | | | | | | | | U.S. government agency securities | 199,510 | | | — | | | 199,510 | | | — | | | U.S. treasury securities | 798,887 | | | — | | | 798,887 | | | — | | | Agency mortgage-backed securities | 274,708 | | | — | | | 274,708 | | | — | | | Agency collateralized mortgage obligations | 33,649 | | | — | | | 33,649 | | | — | | | | | | | | | | | State, county, and municipal securities | 184 | | | — | | | 184 | | | — | | | | | | | | | | | Pooled trust preferred securities issued by banks and insurers | 1,043 | | | — | | | 1,043 | | | — | | | Small business administration pooled securities | 45,763 | | | — | | | 45,763 | | | — | | | Loans held for sale | 3,998 | | | — | | | 3,998 | | | — | | | Derivative instruments | 159,487 | | | — | | | 159,487 | | | — | | | Liabilities | | | | | | | | | Derivative instruments | 204,971 | | | — | | | 204,971 | | | — | | | Total recurring fair value measurements | $ | 1,338,209 | | | $ | 25,951 | | | $ | 1,312,258 | | | $ | — | | | | | | | | | | | Nonrecurring fair value measurements | | | | | | | | | Assets | | | | | | | | | Individually assessed collateral dependent loans (1) | $ | 11,991 | | | $ | — | | | $ | — | | | $ | 11,991 | | | | | | | | | | | Total nonrecurring fair value measurements | $ | 11,991 | | | $ | — | | | $ | — | | | $ | 11,991 | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Fair Value Measurements at Reporting Date Using | | Balance | | Quoted Prices
in Active
Markets for
Identical
Assets
(Level 1) | | Significant
Other
Observable
Inputs
(Level 2) | | Significant
Unobservable
Inputs
(Level 3) | | | December 31, 2022 | | | (Dollars in thousands) | | Recurring fair value measurements | | | | | | | | | Assets | | | | | | | | | Trading securities | $ | 3,888 | | | $ | 3,888 | | | $ | — | | | $ | — | | | Equity securities | 21,119 | | | 21,119 | | | — | | | — | | | Securities available for sale | | | | | | | | | U.S. government agency securities | 202,300 | | | — | | | 202,300 | | | — | | | U.S. treasury securities | 791,341 | | | — | | | 791,341 | | | — | | | Agency mortgage-backed securities | 313,688 | | | — | | | 313,688 | | | — | | | Agency collateralized mortgage obligations | 38,843 | | | — | | | 38,843 | | | — | | | | | | | | | | | State, county, and municipal securities | 191 | | | — | | | 191 | | | — | | | | | | | | | | | Pooled trust preferred securities issued by banks and insurers | 1,034 | | | — | | | 1,034 | | | — | | | Small business administration pooled securities | 51,757 | | | — | | | 51,757 | | | — | | | Loans held for sale | 2,803 | | | — | | | 2,803 | | | — | | | Derivative instruments | 127,958 | | | — | | | 127,958 | | | — | | | Liabilities | | | | | | | | | Derivative instruments | 179,911 | | | — | | | 179,911 | | | — | | | Total recurring fair value measurements, net | $ | 1,375,011 | | | $ | 25,007 | | | $ | 1,350,004 | | | $ | — | | | | | | | | | | | Nonrecurring fair value measurements | | | | | | | | | Assets | | | | | | | | | Individually assessed collateral dependent loans (1) | $ | 16,092 | | | $ | — | | | $ | — | | | $ | 16,092 | | | | | | | | | | | Total nonrecurring fair value measurements | $ | 16,092 | | | $ | — | | | $ | — | | | $ | 16,092 | |
(1) The carrying value of individually assessed collateral dependent loans is based on the lower of amortized cost or fair value of the underlying collateral less costs to sell. The fair value of the underlying collateral is generally determined through independent appraisals, which generally include various Level 3 inputs which are not identifiable. Appraisals may be adjusted by management for qualitative factors such as economic factors and estimated liquidation expenses. The range of these possible adjustments may vary.
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| The estimated fair values and related carrying amounts for assets and liabilities |
The estimated fair values and related carrying amounts for assets and liabilities for which fair value is only disclosed are shown below at the dates indicated: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fair Value Measurements at Reporting Date Using | | | Carrying
Value | | Fair
Value | | Quoted Prices
in Active
Markets for
Identical
Assets
(Level 1) | | Significant
Other
Observable
Inputs
(Level 2) | | Significant
Unobservable
Inputs
(Level 3) | | September 30, 2023 | | | (Dollars in thousands) | | Financial assets | | | | | Securities held to maturity (a) | | | | | | | | | | | U.S. government agency securities | $ | 29,961 | | | $ | 28,342 | | | $ | — | | | $ | 28,342 | | | $ | — | | | U.S. treasury securities | 100,693 | | | 88,331 | | | — | | | 88,331 | | | — | | | Agency mortgage-backed securities | 839,945 | | | 741,995 | | | — | | | 741,995 | | | — | | | Agency collateralized mortgage obligations | 490,011 | | | 404,144 | | | — | | | 404,144 | | | — | | | | | | | | | | | | | Single issuer trust preferred securities issued by banks | 1,500 | | | 1,335 | | | — | | | 1,335 | | | — | | | Small business administration pooled securities | 132,169 | | | 120,283 | | | — | | | 120,283 | | | — | | | | | | | | | | | | | Loans, net of allowance for credit losses (b) | 14,071,675 | | | 13,102,058 | | | — | | | — | | | 13,102,058 | | | Federal Home Loan Bank stock (c) | 43,878 | | | 43,878 | | | — | | | 43,878 | | | — | | | Cash surrender value of life insurance policies (d) | 295,670 | | | 295,670 | | | — | | | 295,670 | | | — | | | Financial liabilities | | | | | | | | | | | Deposit liabilities, other than time deposits (e) | $ | 13,046,763 | | | $ | 13,046,763 | | | $ | — | | | $ | 13,046,763 | | | $ | — | | | Time certificates of deposits (f) | 2,012,763 | | | 1,990,899 | | | — | | | 1,990,899 | | | — | | | Federal Home Loan Bank borrowings (f) | 887,548 | | | 886,799 | | | — | | | 886,799 | | | — | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Junior subordinated debentures (g) | 62,857 | | | 57,347 | | | — | | | 57,347 | | | — | | | Subordinated debentures (f) | 49,957 | | | 45,990 | | | — | | | — | | | 45,990 | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fair Value Measurements at Reporting Date Using | | | Carrying
Value | | Fair
Value | | Quoted Prices
in Active
Markets for
Identical
Assets
(Level 1) | | Significant
Other
Observable
Inputs
(Level 2) | | Significant
Unobservable
Inputs
(Level 3) | | December 31, 2022 | | | (Dollars in thousands) | | Financial assets | | | Securities held to maturity (a) | | | | | | | | | | | U.S. government agency securities | $ | 31,258 | | | $ | 29,036 | | | $ | — | | | $ | 29,036 | | | $ | — | | | U.S. treasury securities | 100,634 | | | 88,879 | | | — | | | 88,879 | | | — | | | Agency mortgage-backed securities | 898,927 | | | 815,952 | | | — | | | 815,952 | | | — | | | Agency collateralized mortgage obligations | 535,971 | | | 458,417 | | | — | | | 458,417 | | | — | | | | | | | | | | | | | Single issuer trust preferred securities issued by banks | 1,500 | | | 1,508 | | | — | | | 1,508 | | | — | | | Small business administration pooled securities | 136,830 | | | 130,918 | | | — | | | 130,918 | | | — | | | | | | | | | | | | | Loans, net of allowance for credit losses (b) | 13,760,164 | | | 13,260,873 | | | — | | | — | | | 13,260,873 | | | Federal Home Loan Bank stock (c) | 5,218 | | | 5,218 | | | — | | | 5,218 | | | — | | | Cash surrender value of life insurance policies (d) | 293,323 | | | 293,323 | | | — | | | 293,323 | | | — | | | Financial liabilities | | | | | | | | | | | Deposit liabilities, other than time deposits (e) | $ | 14,683,266 | | | $ | 14,683,266 | | | $ | — | | | $ | 14,683,266 | | | $ | — | | | Time certificates of deposits (f) | 1,195,741 | | | 1,164,892 | | | — | | | 1,164,892 | | | — | | | Federal Home Loan Bank borrowings (f) | 637 | | | 563 | | | — | | | 563 | | | — | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Junior subordinated debentures (g) | 62,855 | | | 60,002 | | | — | | | 60,002 | | | — | | | Subordinated debentures (f) | 49,885 | | | 45,891 | | | — | | | — | | | 45,891 | |
(a)The fair values presented are based on quoted market prices, where available. If quoted market prices are not available, fair values are based on quoted market prices of comparable instruments and/or discounted cash flow analysis. (b)Fair value of loans is measured using the exit price valuation method, determined primarily by discounting the future cash flows using the current rates at which similar loans would be made to borrowers with similar credit ratings and for the same remaining maturities or cash flows, while incorporating liquidity and credit assumptions. Additionally, this amount excludes individually assessed collateral dependent loans, which are deemed to be marked to fair value on a nonrecurring basis. (c)FHLB stock has no quoted market value and is carried at cost; therefore, the carrying amount approximates fair value. (d)Cash surrender value of life insurance policies is recorded at its cash surrender value (or the amount that can be realized upon surrender of the policy), therefore, carrying amount approximates fair value. (e)Fair value of demand deposits, savings and interest checking accounts and money market deposits is the amount payable on demand at the reporting date. (f)Fair value was determined by discounting anticipated future cash payments using rates currently available for instruments with similar remaining maturities. (g)Fair value was determined based upon market prices of securities with similar terms and maturities.
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