Federal Home Loan Bank Advances - Summary of FHLB Advances (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Federal Home Loan Bank, Advances [Line Items]
FHLB advances (fixed rates 0.13% to 4.96% and variable rates 0.11% to 0.13%) maturing October 2020 to August 2035	$ 2,075,660	$ 1,800,664
ASC 815 fair value hedge and other basis adjustments	11,988	22,183
Federal Home Loan Bank advances	$ 2,087,648	$ 1,822,847
Minimum \| FHLB Advances
Federal Home Loan Bank, Advances [Line Items]
Fixed rates	0.13%
Variable rates	0.11%
Maximum \| FHLB Advances
Federal Home Loan Bank, Advances [Line Items]
Fixed rates	4.96%
Variable rates	0.13%

Carrying value as of the balance sheet date of ASC 815 fair valued hedge and other basis adjustments on long-term debt.

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Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

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-SubTopic 470
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Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

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