Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 64,321	$ 72,276
Interest-bearing deposits	3,120	2,262
Securities available for sale, at fair value	1,089,725	1,309,819
Held-to-maturity Securities	131,780
Other investments	53,347	44,545
Loans Held for sale, Amount	9,817	2,502
Loans and Leases Receivable, Net of Deferred Income	4,490,854	4,457,308
Deposits	4,210,107	4,315,511
Short-term borrowings	1,231,917	1,105,876
Subordinated debt	72,167	72,167
Long-term debt	39,189	89,459
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	64,321	72,276
Interest-bearing deposits	3,120	2,262
Securities available for sale, at fair value	1,089,725	1,309,819
Held-to-maturity Securities	130,454
Other investments	53,347	44,545
Loans Held for sale, Amount	9,817	2,502
Loans and Leases Receivable, Net of Deferred Income	4,509,268	4,439,766
Deposits	4,213,317	4,319,997
Short-term borrowings	1,231,945	1,105,867
Subordinated debt	63,303	62,815
Long-term debt	39,819	90,319
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	64,321	72,276
Interest-bearing deposits	3,120	2,262
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, Fair Value Disclosure [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	1,052,284	1,279,400
Held-to-maturity Securities	130,454
Other investments	53,347	44,545
Loans Held for sale, Amount	9,817	2,502
Loans and Leases Receivable, Net of Deferred Income	31,035	34,864
Deposits	4,213,317	4,319,997
Short-term borrowings	1,231,945	1,105,867
Subordinated debt	0	0
Long-term debt	39,819	90,319
Estimate of Fair Value, Fair Value Disclosure [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	37,441	30,419
Held-to-maturity Securities	0
Other investments	0	0
Loans Held for sale, Amount	0	0
Loans and Leases Receivable, Net of Deferred Income	4,478,233	4,404,902
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	63,303	62,815
Long-term debt	$ 0	$ 0