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Securities (Tables)
 9 Months Ended
Sep. 30, 2025
Investments, Debt and Equity Securities [Abstract]  
Debt Securities, Available-for-sale
The amortized cost and fair value of securities available-for-sale and held-to-maturity at September 30, 2025 and December 31, 2024 are summarized as follows (in thousands):
 Amortized
Cost		Gross
Unrealized
Gains		Gross
Unrealized
Losses		Fair
Value
September 30, 2025:    
Securities available-for-sale:    
U.S. Treasury securities$1,606,437 $46 $12,925 $1,593,558 
U.S. Government agency securities219,925 18 16,127 203,816 
Mortgage-backed securities2,684,056 12,604 78,470 2,618,190 
State and municipal securities1,774,299 3,994 87,755 1,690,538 
Asset-backed securities195 — — 195 
Corporate notes and other314,816 1,976 11,283 305,509 
 $6,599,728 $18,638 $206,560 $6,411,806 
 Amortized
Cost		Gross
Unrealized
Gains		Gross
Unrealized
Losses		Fair
Value
September 30, 2025:    
Securities held-to-maturity:    
U.S. Treasury securities$19,912 $— $448 $19,464 
U.S. Government agency securities255,676 — 6,440 249,236 
Mortgage-backed securities352,571 530 20,455 332,646 
State and municipal securities1,828,121 778 181,161 1,647,738 
Asset-backed securities120,815 22 2,862 117,975 
Corporate notes and other69,414 — 4,405 65,009 
 $2,646,509 $1,330 $215,771 $2,432,068 
Allowance for credit losses - securities held-to-maturity(1,707)
Securities held-to-maturity, net of allowance for credit losses$2,644,802 
Amortized
Cost		Gross
Unrealized
Gains		Gross
Unrealized
Losses		Fair
Value
December 31, 2024:    
Securities available-for-sale:    
U.S. Treasury securities$1,419,727 $28 $14,277 $1,405,478 
U.S. Government agency securities238,636 2 24,572 214,066 
Mortgage-backed securities2,068,950 976 107,567 1,962,359 
State and municipal securities1,537,910 15,382 46,735 1,506,557 
Asset-backed securities45,280 85 27 45,338 
Corporate notes and other476,900 107 28,436 448,571 
 $5,787,403 $16,580 221,614 $5,582,369 
Securities held-to-maturity:    
U.S Treasury securities$19,841 $— $954 $18,887 
U.S. Government agency securities315,286 — 13,719 301,567 
Mortgage-backed securities366,029 6 34,573 331,462 
State and municipal securities1,854,942 1,956 178,744 1,678,154 
Asset-backed securities161,957 41 6,920 155,078 
Corporate notes82,551 — 7,447 75,104 
$2,800,606 $2,003 $242,357 $2,560,252 
Allowance for credit losses - securities held-to-maturity(1,707)
Securities held-to-maturity, net of allowance for credit losses$2,798,899 
Amortized Cost and Fair Value of Debt Securities by Contractual Maturity
The amortized cost and fair value of debt securities as of September 30, 2025 by contractual maturity is shown below. Actual maturities may differ from contractual maturities of mortgage- and asset-backed securities since the mortgages and assets underlying the securities may be called or prepaid with or without penalty. Therefore, these securities are not included in the maturity categories in the following summary (in thousands):
 Available-for-saleHeld-to-maturity
September 30, 2025:Amortized
Cost		Fair
Value		Amortized
 Cost		Fair
Value
Due in one year or less$254,717 $254,763 $19,912 $19,464 
Due in one year to five years153,534 148,861 301,156 292,411 
Due in five years to ten years343,759 329,620 69,337 64,814 
Due after ten years3,163,467 3,060,177 1,782,718 1,604,758 
Mortgage-backed securities2,684,056 2,618,190 352,571 332,646 
Asset-backed securities195 195 120,815 117,975 
 $6,599,728 $6,411,806 $2,646,509 $2,432,068 
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value
At September 30, 2025 and December 31, 2024, the following available-for-sale securities had unrealized losses. The table below classifies these investments according to the term of the unrealized losses of less than twelve months or twelve months or longer (in thousands):
 Investments with an Unrealized Loss of
less than 12 months		Investments with an Unrealized Loss of
12 months or longer		Total Investments with an
Unrealized Loss
 Fair ValueUnrealized LossesFair ValueUnrealized LossesFair ValueUnrealized
Losses
At September 30, 2025      
U.S. Treasury securities$226,406 $3,684 $1,111,559 $9,241 $1,337,965 $12,925 
U.S. Government agency securities1,251 4 198,385 16,123 199,636 16,127 
Mortgage-backed securities530,173 1,955 916,298 76,515 1,446,471 78,470 
State and municipal securities411,231 20,562 991,290 67,193 1,402,521 87,755 
Asset-backed securities195 — — — 195 — 
Corporate notes17,033 39 146,695 11,244 163,728 11,283 
Total temporarily-impaired securities$1,186,289 $26,244 $3,364,227 $180,316 $4,550,516 $206,560 
At December 31, 2024      
U.S. Treasury securities$1,123,453 $12,223 $177,930 $2,054 $1,301,383 $14,277 
U.S. Government agency securities2,347 18 210,127 24,554 212,474 24,572 
Mortgage-backed securities990,956 9,211 607,659 98,356 1,598,615 107,567 
State and municipal securities446,241 5,590 348,807 41,145 795,048 46,735 
Asset-backed securities30,369 27 — — 30,369 27 
Corporate notes131,073 1,215 274,601 27,221 405,674 28,436 
Total temporarily-impaired securities$2,724,439 $28,284 $1,619,124 $193,330 $4,343,563 $221,614