Federal Funds Purchased and Securities Sold Under Agreement to Repurchase - Schedule of Remaining Contractual Maturity in Repurchase Agreements and Collateral Pledged (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements	$ 30,200
Total	30,239	$ 48,073
US Treasury & Agency Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements	30,239
Overnight & Continuous [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total	1,899
Overnight & Continuous [Member] | US Treasury & Agency Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements	1,899
30-90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total	3,900
30-90 Days [Member] | US Treasury & Agency Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements	3,900
Greater Than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total	24,440
Greater Than 90 Days [Member] | US Treasury & Agency Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements	$ 24,440