Federal Funds Purchased and Securities Sold Under Agreements to Repurchase - Schedule of Remaining Contractual Maturity in Repurchase Agreements (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements	$ 29,900	$ 30,200
Total	29,882	30,239
Overnight & Continuous [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total	1,531	1,899
30-90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total		3,900
Greater Than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total	28,351	24,440
US Treasury & Agency Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements	29,882	30,239
US Treasury & Agency Securities [Member] | Overnight & Continuous [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements	1,531	1,899
US Treasury & Agency Securities [Member] | 30-90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements		3,900
US Treasury & Agency Securities [Member] | Greater Than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements, Remaining contractual maturity of the agreements	$ 28,351	$ 24,440