Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 103,602	$ 91,033
Interest-bearing deposits	12,310	24,644
Securities available for sale, at fair value	786,246	778,612
Held-to-maturity Securities	450,886	372,513
Other investments	34,340
Loans Held for sale, Amount	9,785	7,052
Loans and Leases Receivable, Net of Deferred Income	5,374,782	4,879,347
Deposits	5,533,135	4,947,408
Short-term borrowings	846,137	867,943
Subordinated debt	72,167	72,167
Long-term debt	8,458	8,749
Capital Lease Obligations	7,764
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	103,602	91,033
Interest-bearing deposits	12,310	24,644
Securities available for sale, at fair value	786,246	778,612
Held-to-maturity Securities	449,127	368,618
Other investments	34,340	36,498
Loans Held for sale, Amount	9,785	7,052
Loans and Leases Receivable, Net of Deferred Income	5,367,138	4,878,254
Deposits	5,535,206	4,949,714
Short-term borrowings	846,026	867,667
Subordinated debt	65,917	65,656
Long-term debt	8,953	9,169
Capital Lease Obligations	7,764
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	103,602	91,033
Interest-bearing deposits	12,310	24,644
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
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	750,928	743,650
Held-to-maturity Securities	449,127	368,618
Other investments	34,340	36,498
Loans Held for sale, Amount	9,785	7,052
Loans and Leases Receivable, Net of Deferred Income	21,089	18,679
Deposits	5,535,206	4,949,714
Short-term borrowings	846,026	867,667
Subordinated debt	0	0
Long-term debt	8,953	9,169
Capital Lease Obligations	7,764
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	35,318	34,962
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	5,346,049	4,859,575
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	65,917	65,656
Long-term debt	0	$ 0
Capital Lease Obligations	$ 0