Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 100,724	$ 95,934
Interest-bearing deposits	23,168	3,013
Securities available for sale, at fair value	893,101	909,247
Debt Securities, Held-to-maturity	384,909	393,855
Other investments	25,378	32,126
Loans and Leases Receivable, Net of Deferred Income	5,871,070	5,774,139	$ 5,381,305
Deposits	6,130,760	5,897,992
Short-term borrowings	565,616	721,823
Subordinated debt	170,328	170,288
Long-term debt	7,395	7,551
Capital Lease Obligations	7,118	7,217
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	893,101	909,247
Other investments	23,708	30,456
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	100,724	95,934
Interest-bearing deposits	23,168	3,013
Securities available for sale, at fair value	893,101	909,247
Debt Securities, Held-to-maturity	384,909	393,855
Other investments	25,378	32,126
Loans Held for sale, Amount	9,627	11,881
Loans and Leases Receivable, Net of Deferred Income	5,871,070	5,774,139
Deposits	6,130,760	5,897,992
Short-term borrowings	565,616	721,823
Subordinated debt	170,328	170,288
Long-term debt	7,395	7,551
Capital Lease Obligations	7,118	7,217
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	100,724	95,934
Interest-bearing deposits	23,168	3,013
Securities available for sale, at fair value	893,101	909,247
Debt Securities, Held-to-maturity	380,443	383,993
Other investments	25,378	32,126
Loans Held for sale, Amount	9,627	11,881
Loans and Leases Receivable, Net of Deferred Income	5,921,319	5,821,791
Deposits	6,135,980	5,904,147
Short-term borrowings	565,522	721,532
Subordinated debt	169,764	168,067
Long-term debt	7,701	7,720
Capital Lease Obligations	7,118	7,217
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	100,724	95,934
Interest-bearing deposits	23,168	3,013
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	893,101	909,247
Debt Securities, Held-to-maturity	380,443	383,993
Other investments	23,708	30,456
Loans Held for sale, Amount	9,627	11,881
Loans and Leases Receivable, Net of Deferred Income	14,391	15,076
Deposits	6,135,980	5,904,147
Short-term borrowings	565,522	721,532
Subordinated debt	0	0
Long-term debt	7,701	7,720
Capital Lease Obligations	7,118	7,217
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	5,906,928	5,806,715
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	169,764	168,067
Long-term debt	0	0
Capital Lease Obligations	$ 0	$ 0