Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 62,141	$ 66,644
Interest-bearing deposits	11,024	2,808
Securities available for sale, at fair value	890,198	886,560
Held-to-maturity Securities	396,444
Other investments	60,597
Loans Held for sale, Amount	5,849	5,763
Loans and Leases Receivable, Net of Deferred Income	4,798,755	4,683,750
Deposits	4,301,655	4,195,894
Short-term borrowings	1,518,742	1,510,825
Subordinated debt	72,167	72,167
Long-term debt	9,175	9,314
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	62,141	66,644
Interest-bearing deposits	11,024	2,808
Securities available for sale, at fair value	890,198	886,560
Held-to-maturity Securities	400,964
Other investments	60,597	62,952
Loans Held for sale, Amount	5,849	5,763
Loans and Leases Receivable, Net of Deferred Income	4,791,929	4,690,852
Deposits	4,303,085	4,198,817
Short-term borrowings	1,518,561	1,510,718
Subordinated debt	61,208	62,794
Long-term debt	9,999	9,834
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	62,141	66,644
Interest-bearing deposits	11,024	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	854,719	848,732
Held-to-maturity Securities	400,964
Other investments	60,597	62,952
Loans Held for sale, Amount	5,849	5,763
Loans and Leases Receivable, Net of Deferred Income	29,911	30,979
Deposits	4,303,085	4,198,817
Short-term borrowings	1,518,561	1,510,718
Subordinated debt	0	0
Long-term debt	9,999	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	35,479	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	4,762,018	4,659,873
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	61,208	62,794
Long-term debt	$ 0	$ 0