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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).

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The maximum percentage of shareholders' equity of any one issuer other than the U.S. government and its agencies.

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Securities - Additional Information (Detail) $ in Thousands	3 Months Ended
Securities - Additional Information (Detail) $ in Thousands	Mar. 31, 2020 USD ($) Holding	Mar. 31, 2019 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($) Holding
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Maximum percentage of equity of one issuer	10.00%
Number of holdings greater than specified percentage of equity \| Holding	0			0
Equities securities	$ 11,230			$ 12,343
Securities with aggregate fair values	2,100,000			2,000,000
Proceeds from sale of available-for-sale securities	222,668	$ 66,095
Net unrealized gains on available-for-sale securities included in AOCI	58,000			20,700
Accrued interest receivable	43,960			43,648
Federal home loan bank stock, Total	73,900			$ 66,800
Held-to-maturity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Accrued interest receivable	7,200
ASU 2016-13 [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Current expected credit losses to opening retained earnings			$ 200
Grantor Trusts [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Equities securities	$ 7,800