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Investment Securities (Available For Sale Securities Unrealized Gains And Losses, By Security Type) (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 12,097,533,000	$ 8,435,531,000
Available For Sale Securities, Gross Unreailzed Gain at Period End	358,089,000	148,959,000
Available For Sale Securities, Gross Unrealized Loss at Period End	(6,358,000)	(12,864,000)
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
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
Available For Sale Securities, Gross Unreailzed Gain at Period End	62,467,000	23,957,000
Available For Sale Securities, Gross Unrealized Loss at Period End	0	(42,000)
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Fair Value	838,059,000	851,776,000
US Government-sponsored Enterprise Debt Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	50,803,000	138,734,000
Available For Sale Securities, Gross Unreailzed Gain at Period End	3,780,000	730,000
Available For Sale Securities, Gross Unrealized Loss at Period End	(98,000)	(187,000)
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Fair Value	54,485,000	139,277,000
State and municipal obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,968,006,000	1,225,532,000
Available For Sale Securities, Gross Unreailzed Gain at Period End	77,323,000	42,427,000
Available For Sale Securities, Gross Unrealized Loss at Period End	(230,000)	(32,000)
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Fair Value	2,045,099,000	1,267,927,000
Agency mortgage-backed securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	6,557,098,000	3,893,247,000
Available For Sale Securities, Gross Unreailzed Gain at Period End	157,789,000	50,890,000
Available For Sale Securities, Gross Unrealized Loss at Period End	(2,802,000)	(6,173,000)
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Fair Value	6,712,085,000	3,937,964,000
Non-agency mortgage-backed securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	358,074,000	796,451,000
Available For Sale Securities, Gross Unreailzed Gain at Period End	3,380,000	14,036,000
Available For Sale Securities, Gross Unrealized Loss at Period End	(380,000)	(705,000)
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Fair Value	361,074,000	809,782,000
Asset-backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,853,791,000	1,228,151,000
Available For Sale Securities, Gross Unreailzed Gain at Period End	31,125,000	11,056,000
Available For Sale Securities, Gross Unrealized Loss at Period End	(2,673,000)	(5,718,000)
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Fair Value	1,882,243,000	1,233,489,000
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
Available For Sale Securities, Gross Unreailzed Gain at Period End	192,294,000	75,982,000
Available For Sale Securities, Gross Unrealized Loss at Period End	(5,855,000)	(12,596,000)
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Fair Value	8,955,402,000	5,981,235,000
Other Debt Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	534,169,000	325,555,000
Available For Sale Securities, Gross Unreailzed Gain at Period End	22,225,000	5,863,000
Available For Sale Securities, Gross Unrealized Loss at Period End	(175,000)	(7,000)
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Fair Value	$ 556,219,000	$ 331,411,000

X

- Definition

This item represents the gross unrealized gains for securities which are categorized as neither held-to-maturity nor trading securities. Such gross unrealized gains are the excess of the fair value of the Available-for-sale Securities over their carrying value as of the reporting date. Such gross unrealized gains are included in other comprehensive income in the statement of shareholders' equity. This concept represents the balance in unrealized gains at period-end.

+ References

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This item represents the gross unrealized losses for securities which are categorized neither as held-to-maturity nor trading securities. Such gross unrealized losses are the excess of the carrying value of the Available-for-sale Securities over their fair value as of the reporting date. Such gross unrealized losses are included in other comprehensive income in the statement of shareholders' equity. This concept represents the balance in unrealized loss at period end.

+ References

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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-Publisher FASB
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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