Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 65,886	$ 98,624
Interest-bearing deposits	9,736	8,668
Securities available for sale, at fair value	812,877	731,358
Held-to-maturity Securities	410,430	422,096
Other investments	24,400
Loans Held for sale, Amount	9,759	14,850
Loans and Leases Receivable, Net of Deferred Income	5,381,305	5,407,376
Deposits	5,703,522	5,580,705
Short-term borrowings	588,016	707,466
Subordinated debt	72,167	72,167
Long-term debt	8,011	8,161
Capital Lease Obligations	7,498	7,590
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	65,886	98,624
Interest-bearing deposits	9,736	8,668
Securities available for sale, at fair value	812,877	731,358
Held-to-maturity Securities	399,528	418,249
Other investments	24,400	29,837
Loans Held for sale, Amount	9,759	14,850
Loans and Leases Receivable, Net of Deferred Income	5,399,240	5,443,434
Deposits	5,701,021	5,580,812
Short-term borrowings	587,834	707,263
Subordinated debt	70,114	65,785
Long-term debt	8,237	8,548
Capital Lease Obligations	7,498	7,590
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	65,886	98,624
Interest-bearing deposits	9,736	8,668
Securities available for sale, at fair value	0	0
Held-to-maturity Securities	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	797,075	706,042
Held-to-maturity Securities	399,528	418,249
Other investments	24,400	29,837
Loans Held for sale, Amount	9,759	14,850
Loans and Leases Receivable, Net of Deferred Income	26,546	23,249
Deposits	5,701,021	5,580,812
Short-term borrowings	587,834	707,263
Subordinated debt	0	0
Long-term debt	8,237	8,548
Capital Lease Obligations	7,498	7,590
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	15,802	25,316
Held-to-maturity Securities	0	0
Other investments	0	0
Loans Held for sale, Amount	0	0
Loans and Leases Receivable, Net of Deferred Income	5,372,694	5,420,185
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	70,114	65,785
Long-term debt	0	0
Capital Lease Obligations	$ 0	$ 0