Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 92,860	$ 74,427
Interest-bearing deposits	5,151	3,012
Securities available for sale, at fair value	1,347,611	1,318,365
Other investments	44,077	35,444
Loans	4,334,214	4,283,833	4,229,752
Deposits	4,460,421	4,603,863
Short-term borrowings	845,873	626,615
Long-term debt	136,672	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	1,318,037	1,293,422
Other investments	44,077	35,444
Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	29,574	24,943
Other investments	0	0
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	92,860	74,427
Interest-bearing deposits	5,151	3,012
Securities available for sale, at fair value	1,347,611	1,318,365
Other investments	44,077	35,444
Loans	4,334,214	4,283,833
Deposits	4,460,421	4,603,863
Short-term borrowings	845,873	626,615
Long-term debt	136,672	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	92,860	74,427
Interest-bearing deposits	5,151	3,012
Securities available for sale, at fair value	1,347,611	1,318,365
Other investments	44,077	35,444
Loans	4,350,182	4,321,847
Deposits	4,465,990	4,531,685
Short-term borrowings	845,862	626,603
Long-term debt	137,861	145,477
Subordinated debt	61,755	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	92,860	74,427
Interest-bearing deposits	5,151	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	1,318,037	1,293,422
Other investments	44,077	35,444
Loans	27,342	36,903
Deposits	4,465,990	4,531,685
Short-term borrowings	845,862	626,603
Long-term debt	137,861	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	29,574	24,943
Other investments	0	0
Loans	4,322,840	4,284,944
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated debt	$ 61,755	$ 51,706