Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 88,179	$ 98,724
Interest-bearing deposits	5,077	4,258
Securities available for sale	1,291,063	1,171,303
Other investments	33,704	28,228
Loans	4,240,004	4,204,704	4,214,299
Deposits	4,617,801	4,557,881
Short-term borrowings	551,628	356,227
Long-term debt	144,501	174,471
Subordinated debt	72,167	105,750
Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Other investments	0	0
Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Other investments	33,704	28,228
Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Other investments	0	0
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	88,179	98,724
Interest-bearing deposits	5,077	4,258
Securities available for sale	1,291,063	1,171,303
Other investments	33,704	28,228
Loans	4,240,004	4,204,704
Deposits	4,617,801	4,557,881
Short-term borrowings	551,628	356,227
Long-term debt	144,501	174,471
Subordinated debt	72,167	105,750
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	88,179	98,724
Interest-bearing deposits	5,077	4,258
Securities available for sale	1,291,063	1,171,303
Other investments	33,704	28,228
Loans	4,290,985	4,245,114
Deposits	4,548,409	4,493,764
Short-term borrowings	551,619	356,221
Long-term debt	145,654	176,178
Subordinated debt	48,033	76,735
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	88,179	98,724
Interest-bearing deposits	5,077	4,258
Securities available for sale	0	555
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	1,264,186	1,145,955
Other investments	33,704	28,228
Loans	48,673	82,949
Deposits	4,548,409	4,493,764
Short-term borrowings	551,619	356,221
Long-term debt	145,654	176,178
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	26,877	24,793
Other investments	0	0
Loans	4,242,312	4,162,165
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated debt	$ 48,033	$ 76,735