Borrowings - Federal Home Loan Bank Advances (Details) - USD ($)	3 Months Ended	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Collateral securing line of credit	$ 2,781,606,000	$ 958,506,000
Total borrowing capacity remaining	1,276,095,000	760,607,000
Letter of credit pledged	100,000,000	75,000,000
Borrowings against line of credit	0	$ 250,000,000
Weighted average interest rate on outstanding advances		1.60%
Federal Reserve Bank
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Pledged loans to the Federal Reserve Bank	2,463,281,000	$ 1,407,662,000
Line of credit	1,695,639,000	1,013,239,000
Collateral Pledged
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Securities pledged	804,821,000	373,674,000
Collateral Pledged \| Federal Reserve Bank
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Securities pledged	0	4,963,000
FHLB Overnight
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Additional line available	800,000,000	800,000,000
Long Term Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Borrowings against line of credit		150,000,000
90 Day Fixed Rate Advance
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Borrowings against line of credit		$ 100,000,000
Advance term		90 days
FHLB Advance 10 Year
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Borrowings against line of credit		$ 100,000
Advance term		10 years
Early termination costs	$ 6,838,000
FHLB Advance 7 Year
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Borrowings against line of credit		$ 50,000
Advance term		7 years

Long-term Federal Home Loan Bank Advances, Term

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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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The calculated weighted average interest rate for Federal Home Loan Bank advances outstanding as of the Balance Sheet date.

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Amount of advances from the Federal Home Loan Bank (FHLB).

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Amount of advances or credit lines available from the Federal Home Loan Bank (FHLB).

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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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Amount of maximum advances or credit lines available from the Federal Home Loan Bank (FHLB).

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of cash outflow for cost from early extinguishment and prepayment of debt. Includes, but is not limited to, third-party cost, premium paid, and other fee paid to lender directly for debt extinguishment or debt prepayment. Excludes accrued interest.

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The sum of the carrying amounts, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of related debt obligations, primarily secured borrowings and repurchase agreements, and for which the transferees are not permitted to sell or re-pledge them to an unrelated party.

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