Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 53,991	$ 98,724
Interest-bearing deposits	1,780	4,258
Securities available for sale	1,297,203	1,171,303
Other investments	28,357	28,228
Loans	4,218,810	4,204,704	4,128,588
Deposits	4,711,578	4,557,881
Short-term borrowings	308,100	356,227
Long-term debt	174,318	174,471
Subordinated debt	105,750	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	28,357	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	53,991	98,724
Interest-bearing deposits	1,780	4,258
Securities available for sale	1,297,203	1,171,303
Other investments	28,357	28,228
Loans	4,218,810	4,204,704
Deposits	4,711,578	4,557,881
Short-term borrowings	308,100	356,227
Long-term debt	174,318	174,471
Subordinated debt	105,750	105,750
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	53,991	98,724
Interest-bearing deposits	1,780	4,258
Securities available for sale	1,297,203	1,171,303
Other investments	28,357	28,228
Loans	4,291,687	4,245,114
Deposits	4,645,967	4,493,764
Short-term borrowings	308,092	356,221
Long-term debt	176,295	176,178
Subordinated debt	79,539	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	53,991	98,724
Interest-bearing deposits	1,780	4,258
Securities available for sale	513	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	1,270,758	1,145,955
Other investments	28,357	28,228
Loans	57,636	82,949
Deposits	4,645,967	4,493,764
Short-term borrowings	308,092	356,221
Long-term debt	176,295	176,178
Subordinated debt	34,699	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	25,932	24,793
Other investments	0	0
Loans	4,234,051	4,162,165
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated debt	$ 44,840	$ 76,735