Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 78,696	$ 74,427
Interest-bearing deposits	5,374	3,012
Securities available for sale, at fair value	1,332,774	1,318,365
Other investments	50,994	35,444
Loans	4,411,481	4,283,833	4,240,004
Deposits	4,372,388	4,603,863
Short-term borrowings	1,034,967	626,615
Long-term debt	116,539	144,385
Subordinated debt	72,167	72,167
Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	0	0
Other investments	0	0
Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	1,301,898	1,293,422
Other investments	50,994	35,444
Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	30,876	24,943
Other investments	0	0
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	78,696	74,427
Interest-bearing deposits	5,374	3,012
Securities available for sale, at fair value	1,332,774	1,318,365
Other investments	50,994	35,444
Loans	4,411,481	4,283,833
Deposits	4,372,388	4,603,863
Short-term borrowings	1,034,967	626,615
Long-term debt	116,539	144,385
Subordinated debt	72,167	72,167
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	78,696	74,427
Interest-bearing deposits	5,374	3,012
Securities available for sale, at fair value	1,332,774	1,318,365
Other investments	50,994	35,444
Loans	4,391,765	4,321,847
Deposits	4,376,654	4,531,685
Short-term borrowings	1,034,917	626,603
Long-term debt	117,655	145,477
Subordinated debt	62,714	51,706
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	78,696	74,427
Interest-bearing deposits	5,374	3,012
Securities available for sale, at fair value	0	0
Other investments	0	0
Loans	0	0
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated 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	1,301,898	1,293,422
Other investments	50,994	35,444
Loans	27,037	36,903
Deposits	4,376,654	4,531,685
Short-term borrowings	1,034,917	626,603
Long-term debt	117,655	145,477
Subordinated debt	0	0
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	30,876	24,943
Other investments	0	0
Loans	4,364,728	4,284,944
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated debt	$ 62,714	$ 51,706