Fair Value of Financial Instruments - Changes in the Level 3 Fair Value Category of Unobservable Inputs (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
State and Local Governments Tax-Exempt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 1,835	$ 2,108	$ 2,071	$ 2,307
Change in Fair Value	$ (4)	(19)	5	(58)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent
Payments & Maturities			(245)	(160)
Ending Balance	$ 1,831	2,089	1,831	2,089
State and Local Governments Taxable[Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,305	1,394	1,274	2,466
Change in Fair Value	$ (27)	(69)	4	(152)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent
Reclassification & Adjustments				(989)
Ending Balance	$ 1,278	1,325	1,278	1,325
State and Local Governments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	3,140	3,502	3,345	4,773
Change in Fair Value	$ (31)	(88)	0	(210)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent
Payments & Maturities			(245)	(160)
Reclassification & Adjustments				(989)
Ending Balance	$ 3,109	$ 3,414	$ 3,109	$ 3,414