Allowance for Credit Losses (Held-to-Maturity Debt Securities by Credit Quality Indication) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	$ 579,197	$ 1,134,400
Less: Allowance for credit losses	(59)	0
Held-to-maturity securities, net of allowance for credit losses	579,138	1,134,400
U.S. Government agencies
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	124,575
2019	0
2018	50,000
2017	0
2016	0
Prior	3,384
Amortized Cost	177,959	902,974
U.S. Government agencies \| 1-4 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	124,575
2019	0
2018	50,000
2017	0
2016	0
Prior	3,384
Amortized Cost	177,959
U.S. Government agencies \| 5-7 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Amortized Cost	0
U.S. Government agencies \| 8-10 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Amortized Cost	0
Municipal
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	0
2019	161
2018	7,570
2017	43,633
2016	10,139
Prior	139,204
Amortized Cost	200,707	231,426
Municipal \| 1-4 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	0
2019	161
2018	7,570
2017	43,633
2016	10,139
Prior	139,204
Amortized Cost	200,707
Municipal \| 5-7 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Amortized Cost	0
Municipal \| 8-10 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Amortized Cost	0
Mortgage-backed securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	200,531
2019	0
2018	0
2017	0
2016	0
Prior	0
Amortized Cost	200,531	$ 0
Mortgage-backed securities \| 1-4 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	200,531
2019	0
2018	0
2017	0
2016	0
Prior	0
Amortized Cost	200,531
Mortgage-backed securities \| 5-7 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Amortized Cost	0
Mortgage-backed securities \| 8-10 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Amortized Cost	$ 0

Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Amount of investment in debt security measured at amortized cost (held-to-maturity) originated more than five years prior to current fiscal year.

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Amount of investment in debt security measured at amortized cost (held-to-maturity) originated four years prior to current fiscal year.

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Amount of investment in debt security measured at amortized cost (held-to-maturity) originated in current fiscal year.

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Amount of investment in debt security measured at amortized cost (held-to-maturity) originated three years prior to current fiscal year.

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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