Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 11,457,305,000	$ 13,738,206,000
Fair Value	9,860,828,000	12,238,316,000
U.S. government and federal agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	988,175,000	1,078,807,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost	599,278,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	211,650,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Amortized Cost	177,247,000
Fair Value	947,976,000	1,035,406,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value	588,709,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value	199,843,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Fair Value	159,424,000
Government-sponsored enterprise obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	55,666,000	55,729,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Amortized Cost	4,948,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost	50,718,000
Fair Value	40,593,000	43,108,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Fair Value	4,293,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	36,300,000
State and municipal obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,381,574,000	1,965,028,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost	76,664,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	373,467,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Amortized Cost	792,381,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost	139,062,000
Fair Value	1,178,414,000	1,767,109,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value	75,389,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value	338,785,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Fair Value	648,198,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	116,042,000
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,722,758,000	5,087,893,000
Fair Value	3,792,567,000	4,308,427,000
Non-Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,353,003,000	1,423,469,000
Fair Value	1,137,448,000	1,211,607,000
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,441,736,000	3,588,025,000
Fair Value	2,313,545,000	3,397,801,000
Total Mortgage And Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,517,497,000	10,099,387,000
Fair Value	7,243,560,000	8,917,835,000
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	514,393,000	539,255,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost	50,120,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	206,375,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Amortized Cost	244,638,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost	13,260,000
Fair Value	450,285,000	$ 474,858,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value	48,876,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value	190,217,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Fair Value	200,148,000
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	$ 11,044,000