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Securities - Additional Information (Details) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2021 USD ($) Investment	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) Investment	Dec. 31, 2019 USD ($) Investment	Dec. 31, 2018 USD ($)
Schedule of Investments [Line Items]
Federal Home Loan Bank stock, at cost | $	[1]	$ 698,984		$ 714,005	$ 647,562
Net gains on equity securities | $		$ 483,000	$ 215,000	$ 582,000	$ 2,300	$ 2,000
Collateralized Mortgage Obligations
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more		4		4	3
Capital Trust Notes
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more		5		5	5
Asset-backed Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more		5		7	3
Corporate Bonds
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more		5		3	2
Municipal Bonds
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more		1		1	1
US Government Agencies Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more					7
Mortgage-Related Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more					3
Mutual Fund
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more					1
[1] Carrying value and estimated fair value are at cost.

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Number of Securities, Continuous Unrealized Loss Position More Than Twelve Months

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- Definition

Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117546-209714

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- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 325
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809

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