Securities - Gross Unrealized Losses, Aggregated by Investment Category and Length of Time (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	$ (3,736)	$ (140)
Fair Value, Less Than Twelve Months	244,115	51,893
Gross Unrealized Losses, Total	(3,736)	(140)
Fair Value, Total	244,115	51,893
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	(630)
Fair Value, Less Than Twelve Months	53,192
Gross Unrealized Losses, Total	(630)
Fair Value, Total	53,192
U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	(1,832)	(130)
Fair Value, Less Than Twelve Months	104,211	48,331
Gross Unrealized Losses, Total	(1,832)	(130)
Fair Value, Total	104,211	48,331
Mortgage-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	(1,075)
Fair Value, Less Than Twelve Months	72,504
Gross Unrealized Losses, Total	(1,075)
Fair Value, Total	72,504
State and Local Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	(199)	(10)
Fair Value, Less Than Twelve Months	14,208	3,562
Gross Unrealized Losses, Total	(199)	(10)
Fair Value, Total	$ 14,208	$ 3,562