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Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 12,097,533,000	$ 8,435,531,000
Debt Securities, Available-for-sale, Fair Value		12,449,264,000	8,571,626,000
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		775,592,000	827,861,000
Debt Securities, Available-for-sale, Fair Value		$ 838,059,000	851,776,000
Weighted Average Yield	[1]	1.66%
U.S. Government And Federal Agency Obligations [Member] | Maturity Within 1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 59,627,000
Debt Securities, Available-for-sale, Fair Value		$ 59,641,000
Weighted Average Yield	[1]	0.90%
U.S. Government And Federal Agency Obligations [Member] | Maturity After 1 But Within 5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 490,333,000
Debt Securities, Available-for-sale, Fair Value		$ 521,540,000
Weighted Average Yield	[1]	2.22%
U.S. Government And Federal Agency Obligations [Member] | Maturity After 5 But Within 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 225,632,000
Debt Securities, Available-for-sale, Fair Value		$ 256,878,000
Weighted Average Yield	[1]	0.65%
US Government-sponsored Enterprise Debt Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 50,803,000	138,734,000
Debt Securities, Available-for-sale, Fair Value		$ 54,485,000	139,277,000
Weighted Average Yield		2.32%
US Government-sponsored Enterprise Debt Securities [Member] | Maturity Within 1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 14,993,000
Debt Securities, Available-for-sale, Fair Value		$ 14,916,000
Weighted Average Yield		2.15%
US Government-sponsored Enterprise Debt Securities [Member] | Maturity After 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 35,810,000
Debt Securities, Available-for-sale, Fair Value		$ 39,569,000
Weighted Average Yield		2.39%
State and municipal obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 1,968,006,000	1,225,532,000
Debt Securities, Available-for-sale, Fair Value		$ 2,045,099,000	1,267,927,000
Weighted Average Yield		2.06%
State and municipal obligations [Member] | Maturity Within 1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 34,694,000
Debt Securities, Available-for-sale, Fair Value		$ 34,866,000
Weighted Average Yield		2.35%
State and municipal obligations [Member] | Maturity After 1 But Within 5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 865,165,000
Debt Securities, Available-for-sale, Fair Value		$ 901,201,000
Weighted Average Yield		2.20%
State and municipal obligations [Member] | Maturity After 5 But Within 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 595,510,000
Debt Securities, Available-for-sale, Fair Value		$ 627,063,000
Weighted Average Yield		2.01%
State and municipal obligations [Member] | Maturity After 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 472,637,000
Debt Securities, Available-for-sale, Fair Value		$ 481,969,000
Weighted Average Yield		1.84%
Agency mortgage-backed securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 6,557,098,000	3,893,247,000
Debt Securities, Available-for-sale, Fair Value		$ 6,712,085,000	3,937,964,000
Weighted Average Yield		2.00%
Non-agency mortgage-backed securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 358,074,000	796,451,000
Debt Securities, Available-for-sale, Fair Value		$ 361,074,000	809,782,000
Weighted Average Yield		2.39%
Asset-backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 1,853,791,000	1,228,151,000
Debt Securities, Available-for-sale, Fair Value		$ 1,882,243,000	1,233,489,000
Weighted Average Yield		1.53%
Total mortgage and asset-backed securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 8,768,963,000	5,917,849,000
Debt Securities, Available-for-sale, Fair Value		$ 8,955,402,000	5,981,235,000
Weighted Average Yield		1.92%
Other Debt Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 534,169,000	325,555,000
Debt Securities, Available-for-sale, Fair Value		556,219,000	$ 331,411,000
Other Debt Securities [Member] | Maturity Within 1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		8,041,000
Debt Securities, Available-for-sale, Fair Value		8,118,000
Other Debt Securities [Member] | Maturity After 1 But Within 5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		254,173,000
Debt Securities, Available-for-sale, Fair Value		265,486,000
Other Debt Securities [Member] | Maturity After 5 But Within 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		240,759,000
Debt Securities, Available-for-sale, Fair Value		250,036,000
Other Debt Securities [Member] | Maturity After 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		31,196,000
Debt Securities, Available-for-sale, Fair Value		$ 32,579,000
[1] Rate does not reflect inflation adjustment on inflation-protected securities

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