Investment Securities - Investment Ratings of All Privately Issued Mortgage-Backed Securities and Other Debt Securities (Detail) $ in Thousands	Dec. 31, 2020 USD ($)
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Amortized Cost	$ 218,014
Total securities with disclosed rating, Estimated Fair Value	204,504
A or Better [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	10,375
BBB [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	62,016
BB [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	31,303
B or Less [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	490
Not Rated [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	100,320
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Amortized Cost	1,531
Total securities with disclosed rating, Estimated Fair Value	1,540
Obligations of States and Political Subdivisions [Member] | A or Better [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	1,540
Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Amortized Cost	77,171
Total securities with disclosed rating, Estimated Fair Value	70,289
Privately Issued [Member] | A or Better [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	1,533
Privately Issued [Member] | B or Less [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	490
Privately Issued [Member] | Not Rated [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	68,266
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Amortized Cost	139,312
Total securities with disclosed rating, Estimated Fair Value	132,675
Other Debt Securities [Member] | A or Better [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	7,302
Other Debt Securities [Member] | BBB [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	62,016
Other Debt Securities [Member] | BB [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	31,303
Other Debt Securities [Member] | Not Rated [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	$ 32,054