Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 75,160	$ 91,033
Interest-bearing deposits	47,944	24,644
Securities available for sale, at fair value	832,754	778,612
Held-to-maturity Securities	386,954	372,513
Other investments	38,669
Loans Held for sale, Amount	9,588	7,052
Loans and Leases Receivable, Net of Deferred Income	4,907,961	4,879,347
Deposits	4,969,729	4,947,408
Short-term borrowings	961,601	867,943
Subordinated debt	72,167	72,167
Long-term debt	8,604	8,749
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	75,160	91,033
Interest-bearing deposits	47,944	24,644
Securities available for sale, at fair value	832,754	778,612
Held-to-maturity Securities	383,735	368,618
Other investments	38,669	36,498
Loans Held for sale, Amount	9,588	7,052
Loans and Leases Receivable, Net of Deferred Income	4,890,426	4,878,254
Deposits	4,971,049	4,949,714
Short-term borrowings	961,449	867,667
Subordinated debt	63,964	65,656
Long-term debt	9,038	9,169
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	75,160	91,033
Interest-bearing deposits	47,944	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
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	797,343	743,650
Held-to-maturity Securities	383,735	368,618
Other investments	38,669	36,498
Loans Held for sale, Amount	9,588	7,052
Loans and Leases Receivable, Net of Deferred Income	22,010	18,679
Deposits	4,971,049	4,949,714
Short-term borrowings	961,449	867,667
Subordinated debt	0	0
Long-term debt	9,038	9,169
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	35,411	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	4,868,416	4,859,575
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	63,964	65,656
Long-term debt	$ 0	$ 0