Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 94,579	$ 100,009
Interest-bearing deposits	240,095	256,572
Securities available for sale, at fair value	1,124,956	831,223
Debt Securities, Held-to-maturity	548,057	361,844
Other investments	12,719	12,227
Loans and Leases Receivable, Net of Deferred Income	6,732,580	6,761,183	$ 6,949,716
Deposits	7,936,485	7,438,666
Short-term borrowings	117,754	117,373
Subordinated debt	170,734	170,612
Long-term debt	5,746	56,258
Capital Lease Obligations	6,039	6,385
Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	0	0
Other investments	0	0
Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	1,124,956	831,223
Other investments	11,049	10,557
Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	0	0
Other investments	1,670	1,670
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	94,579	100,009
Interest-bearing deposits	240,095	256,572
Securities available for sale, at fair value	1,124,956	831,223
Debt Securities, Held-to-maturity	548,057	361,844
Other investments	12,719	12,227
Loans Held for sale, Amount	19,925	33,436
Loans and Leases Receivable, Net of Deferred Income	6,732,580	6,761,183
Deposits	7,936,485	7,438,666
Short-term borrowings	117,754	117,373
Subordinated debt	170,734	170,612
Long-term debt	5,746	56,258
Capital Lease Obligations	6,039	6,385
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	94,579	100,009
Interest-bearing deposits	240,095	256,572
Securities available for sale, at fair value	1,124,956	831,223
Debt Securities, Held-to-maturity	547,343	369,851
Other investments	12,719	12,227
Loans Held for sale, Amount	19,925	33,436
Loans and Leases Receivable, Net of Deferred Income	7,118,886	7,202,763
Deposits	7,936,033	7,440,906
Short-term borrowings	117,602	117,037
Subordinated debt	175,178	165,665
Long-term debt	6,385	57,881
Capital Lease Obligations	6,039	6,385
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	94,579	100,009
Interest-bearing deposits	240,095	256,572
Securities available for sale, at fair value	0	0
Debt Securities, Held-to-maturity	0	0
Other investments	0	0
Loans Held for sale, Amount	0	0
Loans and Leases Receivable, Net of Deferred Income	0	0
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	0	0
Long-term debt	0	0
Capital Lease Obligations	0	0
Estimate of Fair Value Measurement [Member] | Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	0	0
Interest-bearing deposits	0	0
Securities available for sale, at fair value	1,124,956	831,223
Debt Securities, Held-to-maturity	547,343	369,851
Other investments	11,049	10,557
Loans Held for sale, Amount	19,925	33,436
Loans and Leases Receivable, Net of Deferred Income	24,512	35,543
Deposits	7,936,033	7,440,906
Short-term borrowings	117,602	117,037
Subordinated debt	0	0
Long-term debt	6,385	57,881
Capital Lease Obligations	6,039	6,385
Estimate of Fair Value Measurement [Member] | Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	0	0
Interest-bearing deposits	0	0
Securities available for sale, at fair value	0	0
Debt Securities, Held-to-maturity	0	0
Other investments	1,670	1,670
Loans Held for sale, Amount	0	0
Loans and Leases Receivable, Net of Deferred Income	7,094,374	7,167,220
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	175,178	165,665
Long-term debt	0	0
Capital Lease Obligations	$ 0	$ 0