Investment Securities - (ASU 2016-13 Adoption Impact) (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	$ (87)	$ 70	$ 0
Cumulative Effect, Period of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		70
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		70
Corporate Obligations
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	$ (6)		0
Corporate Obligations | Cumulative Effect, Period of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		6
Corporate Obligations | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		6
Municipal Notes
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses			$ 0
Municipal Notes | Cumulative Effect, Period of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		64
Municipal Notes | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		$ 64