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Debt Securities, Securities Issued With Full Faith And Credit Guarantees, Percentage

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Number Of Government Sponsored Securities

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Number Of Mortgage-Backed Securities

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Number Of Mortgage-Backed Securities With Unrealized Losses

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Par Value Of Mortgage-Backed Securities Pledged To FRB

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Vertical Risk Retention, Percentage

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Amount of affordable housing tax credits and other tax benefits recognized.

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Amount of investment in qualified affordable housing projects.

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Amount of amortization expense of investment in qualified affordable housing projects.

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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).

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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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).

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Investments - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2018 USD ($) security	Dec. 31, 2020 USD ($) security numberOfInvestments	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($)
Investment Holdings [Line Items]
Amortized Cost				$ 1,986,957	$ 485,756
Vertical risk retention interest	500.00%			5.00%
Par value of mortgage-backed securities pledged to FRB				$ 815,000	252,000
Gain on equity securities investment		$ 8,000
Non-marketable securities investment				26,000
Low income housing tax credit investments				6,000	6,000	$ 4,000
Amount of amortization reported in income tax expense				5,000	4,000	$ 4,000
Total carrying value of LIHTC investments				54,000	58,000
Liability for unfunded commitments				$ 19,000	29,000
Minimum
Investment Holdings [Line Items]
Number of government sponsored securities with unrealized losses \| numberOfInvestments				8
Maximum
Investment Holdings [Line Items]
Number of government sponsored securities with unrealized losses \| numberOfInvestments				10
Student Loan
Investment Holdings [Line Items]
Private education loans sold	$ 1,700,000
Mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost				$ 308,913	$ 215,888
Number of mortgage-backed securities sold \| security			9
Proceeds from sale of securities			$ 41,000
Recognized loss from sale of securities			$ 2,000
Number of mortgage-backed securities with unrealized losses \| security				6	33
Mortgage-backed securities were issued under Ginnie Mae programs that carry a full faith and credit guarantee from the U.S. Government				32.00%
Number of mortgage-backed securities \| security					107
Utah Housing Corporation bonds
Investment Holdings [Line Items]
Amortized Cost				$ 12,357	$ 19,474
Utah Housing Corporation bonds \| Aa3 Rating
Investment Holdings [Line Items]
Amortized Cost				12,000	19,000
U.S. government-sponsored enterprises and Treasuries
Investment Holdings [Line Items]
Amortized Cost				$ 1,596,890	$ 250,394
Number of government sponsored securities with unrealized losses \| security				0
Number of government sponsored securities \| security				30
Government National Mortgage Association Certificates and Obligations (GNMA) \| Mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost				$ 32,000
Number of mortgage-backed securities with unrealized losses \| security					18
Federal National Mortgage Association Certificates and Obligations (FNMA) \| Mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost				80,000
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) \| Mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost				$ 197,000