Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 76,456	$ 66,644
Interest-bearing deposits	5,097	2,808
Securities available for sale, at fair value	813,659	886,560
Held-to-maturity Securities	389,513
Other investments	54,066
Loans Held for sale, Amount	7,855	5,763
Loans and Leases Receivable, Net of Deferred Income	4,860,652	4,683,750
Deposits	4,458,980	4,195,894
Short-term borrowings	1,330,327	1,510,825
Subordinated debt	72,167	72,167
Long-term debt	8,892	9,314
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	76,456	66,644
Interest-bearing deposits	5,097	2,808
Securities available for sale, at fair value	813,659	886,560
Held-to-maturity Securities	396,994
Other investments	54,066	62,952
Loans Held for sale, Amount	7,855	5,763
Loans and Leases Receivable, Net of Deferred Income	4,882,076	4,690,852
Deposits	4,461,516	4,198,817
Short-term borrowings	1,329,740	1,510,718
Subordinated debt	63,858	62,794
Long-term debt	9,840	9,834
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	76,456	66,644
Interest-bearing deposits	5,097	2,808
Securities available for sale, at fair value	0	0
Held-to-maturity Securities	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
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	776,380	848,732
Held-to-maturity Securities	396,994
Other investments	54,066	62,952
Loans Held for sale, Amount	7,855	5,763
Loans and Leases Receivable, Net of Deferred Income	28,158	30,979
Deposits	4,461,516	4,198,817
Short-term borrowings	1,329,740	1,510,718
Subordinated debt	0	0
Long-term debt	9,840	9,834
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	37,279	37,828
Held-to-maturity Securities	0
Other investments	0	0
Loans Held for sale, Amount	0	0
Loans and Leases Receivable, Net of Deferred Income	4,853,918	4,659,873
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	63,858	62,794
Long-term debt	$ 0	$ 0