Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 91,033,000	$ 66,644,000
Interest-bearing deposits	24,644,000	2,808,000
Securities available for sale	778,612,000	886,560,000
Held-to-maturity Securities	372,513,000	384,324,000
Other investments	36,498,000	62,952,000
Loans held for sale	7,052,000	5,763,000
Loans	4,879,347,000	4,683,750,000	$ 4,457,308,000
Deposits	4,947,408,000	4,195,894,000
Short-term borrowings	867,943,000	1,510,825,000	$ 1,105,876,000
Long-term debt	8,749,000	9,314,000
Subordinated debt	72,167,000	72,167,000
Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale	0	0
Other investments	0	0
Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale	743,650,000	848,732,000
Other investments	36,498,000	62,952,000
Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale	34,962,000	37,828,000
Other investments	0	0
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	91,033,000	66,644,000
Interest-bearing deposits	24,644,000	2,808,000
Securities available for sale	778,612,000	886,560,000
Held-to-maturity Securities	372,513,000	384,324,000
Other investments	36,498,000	62,952,000
Loans held for sale	7,052,000	5,763,000
Loans	4,879,347,000	4,683,750,000
Deposits	4,947,408,000	4,195,894,000
Short-term borrowings	867,943,000	1,510,825,000
Long-term debt	8,749,000	9,314,000
Subordinated debt	72,167,000	72,167,000
Estimated Fair Value [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	91,033,000	66,644,000
Interest-bearing deposits	24,644,000	2,808,000
Securities available for sale	778,612,000	886,560,000
Held-to-maturity Securities	368,618,000	382,341,000
Other investments	36,498,000	62,952,000
Loans held for sale	7,052,000	5,763,000
Loans	4,878,254,000	4,690,852,000
Deposits	4,949,714,000	4,198,817,000
Short-term borrowings	867,667,000	1,510,718,000
Long-term debt	9,169,000	9,834,000
Subordinated debt	65,656,000	62,794,000
Estimated Fair Value [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	91,033,000	66,644,000
Interest-bearing deposits	24,644,000	2,808,000
Securities available for sale	0	0
Held-to-maturity Securities	0	0
Other investments	0	0
Loans held for sale	0	0
Loans	0	0
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated debt	0	0
Estimated Fair Value [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	743,650,000	848,732,000
Held-to-maturity Securities	368,618,000	382,341,000
Other investments	36,498,000	62,952,000
Loans held for sale	7,052,000	5,763,000
Loans	18,679,000	30,979,000
Deposits	4,949,714,000	4,198,817,000
Short-term borrowings	867,667,000	1,510,718,000
Long-term debt	9,169,000	9,834,000
Subordinated debt	0	0
Estimated Fair Value [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	34,962,000	37,828,000
Held-to-maturity Securities	0	0
Other investments	0	0
Loans held for sale	0	0
Loans	4,859,575,000	4,659,873,000
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated debt	$ 65,656,000	$ 62,794,000