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Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($)
Mar. 31, 2026
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost $ 9,333,626,000 $ 9,742,278,000
Fair Value 8,646,127,000 9,095,513,000
U.S. government and federal agency obligations    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 3,147,185,000 3,257,561,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost 422,299,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost 1,704,983,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Amortized Cost 913,297,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost 106,606,000  
Fair Value 3,147,293,000 3,279,100,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value 423,185,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value 1,707,211,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Fair Value 910,616,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value 106,281,000  
Government-sponsored enterprise obligations    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 54,599,000 54,951,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost 3,962,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Amortized Cost 30,816,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost 19,821,000  
Fair Value 43,985,000 44,712,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value 3,737,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Fair Value 26,321,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value 13,927,000  
State and municipal obligations [Member]    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 705,864,000 715,037,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost 55,782,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost 428,431,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Amortized Cost 116,777,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost 104,874,000  
Fair Value 654,824,000 664,733,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value 55,348,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value 409,208,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Fair Value 103,102,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value 87,166,000  
Agency mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 3,701,146,000 3,786,811,000
Fair Value 3,123,669,000 3,223,105,000
Non-Agency Mortgage-Backed Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 446,168,000 467,200,000
Fair Value 414,777,000 435,688,000
Asset-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 1,104,943,000 1,269,503,000
Fair Value 1,093,819,000 1,262,045,000
Total Mortgage And Asset-Backed Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 5,252,257,000 5,523,514,000
Fair Value 4,632,265,000 4,920,838,000
Other debt securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 173,721,000 191,215,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost 8,021,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost 59,891,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Amortized Cost 81,872,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost 23,937,000  
Fair Value 167,760,000 $ 186,130,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value 7,924,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value 55,915,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Fair Value 80,151,000  
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value $ 23,770,000