Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 77,485	$ 98,724
Interest-bearing deposits	4,497	4,258
Securities available for sale	1,306,687	1,171,303
Other investments	33,913	28,228
Loans	4,229,752	4,204,704	4,159,531
Deposits	4,733,047	4,557,881
Short-term borrowings	441,848	356,227
Long-term debt	144,615	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	33,913	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	77,485	98,724
Interest-bearing deposits	4,497	4,258
Securities available for sale	1,306,687	1,171,303
Other investments	33,913	28,228
Loans	4,229,752	4,204,704
Deposits	4,733,047	4,557,881
Short-term borrowings	441,848	356,227
Long-term debt	144,615	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	77,485	98,724
Interest-bearing deposits	4,497	4,258
Securities available for sale	1,306,687	1,171,303
Other investments	33,913	28,228
Loans	4,276,416	4,245,114
Deposits	4,664,831	4,493,764
Short-term borrowings	441,838	356,221
Long-term debt	145,721	176,178
Subordinated debt	47,833	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	77,485	98,724
Interest-bearing deposits	4,497	4,258
Securities available for sale	688	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	1,278,710	1,145,955
Other investments	33,913	28,228
Loans	55,903	82,949
Deposits	4,664,831	4,493,764
Short-term borrowings	441,838	356,221
Long-term debt	145,721	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	27,289	24,793
Other investments	0	0
Loans	4,220,513	4,162,165
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated debt	$ 47,833	$ 76,735