Investment Securities Available for Sale (Narrative) (Details)	3 Months Ended
Mar. 31, 2021 USD ($) securities	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Financing Receivable, Impaired [Line Items]
Investment securities gains, net	$ (1,990,000)	$ 8,734,000
Gross losses	1,990,000	0
Gross realized gains on sales	$ 0	8,734,000
Investment securities in a loss position for less than twelve months \| securities	115
Investment securities in a loss position for twelve months or longer \| securities	0
Investment securities gains, net	$ (1,990,000)	$ 8,734,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Collateral Pledged
Financing Receivable, Impaired [Line Items]
Pledged to secure deposits	$ 3,840,000,000		$ 3,840,000,000

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).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of realized gain 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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Amount of restricted 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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