Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 69,235	$ 72,276
Interest-bearing deposits	3,529	2,262
Securities available for sale, at fair value	1,050,733	1,309,819
Held-to-maturity Securities	154,035
Other investments	53,976	44,545
Loans Held for sale, Amount	4,986	2,502
Loans and Leases Receivable, Net of Deferred Income	4,575,735	4,457,308
Deposits	4,161,490	4,315,511
Short-term borrowings	1,329,794	1,105,876
Subordinated debt	72,167	72,167
Long-term debt	39,052	89,459
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	69,235	72,276
Interest-bearing deposits	3,529	2,262
Securities available for sale, at fair value	1,050,733	1,309,819
Held-to-maturity Securities	154,837
Other investments	53,976	44,545
Loans Held for sale, Amount	4,986	2,502
Loans and Leases Receivable, Net of Deferred Income	4,596,889	4,439,766
Deposits	4,164,660	4,319,997
Short-term borrowings	1,329,920	1,105,867
Subordinated debt	62,227	62,815
Long-term debt	39,704	90,319
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	69,235	72,276
Interest-bearing deposits	3,529	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 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	1,013,034	1,279,400
Held-to-maturity Securities	154,837
Other investments	53,976	44,545
Loans Held for sale, Amount	4,986	2,502
Loans and Leases Receivable, Net of Deferred Income	26,916	34,864
Deposits	4,164,660	4,319,997
Short-term borrowings	1,329,920	1,105,867
Subordinated debt	0	0
Long-term debt	39,704	90,319
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	37,699	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	4,569,973	4,404,902
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	62,227	62,815
Long-term debt	$ 0	$ 0