Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 101,744	$ 98,624
Interest-bearing deposits	2,237	8,668
Securities available for sale, at fair value	851,243	731,358
Debt Securities, Held-to-maturity	403,019	422,096
Other investments	25,327	29,837
Loans and Leases Receivable, Net of Deferred Income	5,640,106	5,407,376	$ 5,374,782
Deposits	5,913,574	5,580,705
Short-term borrowings	545,187	707,466
Subordinated debt	170,304	72,167
Long-term debt	7,859	8,161
Capital Lease Obligations	7,405	7,590
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	849,573	706,042
Other investments	25,327	29,837
Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	1,670	25,316
Other investments	0	0
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	101,744	98,624
Interest-bearing deposits	2,237	8,668
Securities available for sale, at fair value	851,243	731,358
Debt Securities, Held-to-maturity	403,019	422,096
Other investments	25,327
Loans Held for sale, Amount	7,038	14,850
Loans and Leases Receivable, Net of Deferred Income	5,640,106	5,407,376
Deposits	5,913,574	5,580,705
Short-term borrowings	545,187	707,466
Subordinated debt	170,304	72,167
Long-term debt	7,859	8,161
Capital Lease Obligations	7,405	7,590
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	101,744	98,624
Interest-bearing deposits	2,237	8,668
Securities available for sale, at fair value	851,243	731,358
Debt Securities, Held-to-maturity	390,168	418,249
Other investments	25,327	29,837
Loans Held for sale, Amount	7,038	14,850
Loans and Leases Receivable, Net of Deferred Income	5,648,478	5,443,434
Deposits	5,913,538	5,580,812
Short-term borrowings	545,095	707,263
Subordinated debt	170,561	65,785
Long-term debt	8,012	8,548
Capital Lease Obligations	7,405	7,590
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	101,744	98,624
Interest-bearing deposits	2,237	8,668
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	849,573	706,042
Debt Securities, Held-to-maturity	390,168	418,249
Other investments	25,327	29,837
Loans Held for sale, Amount	7,038	14,850
Loans and Leases Receivable, Net of Deferred Income	12,864	23,249
Deposits	5,913,538	5,580,812
Short-term borrowings	545,095	707,263
Subordinated debt	0	0
Long-term debt	8,012	8,548
Capital Lease Obligations	7,405	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	1,670	25,316
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	5,635,614	5,420,185
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	170,561	65,785
Long-term debt	0	0
Capital Lease Obligations	$ 0	$ 0