Fair Values of Assets and Liabilities - Schedule of Assets Measured on Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets		$ 1,216,011
Fair Value, Measurements, Non-recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	65,592	89,776
Other real estate owned	11,604	12,228
Total Assets	77,196	102,004
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets	513	555
Level 1 [Member] | Fair Value, Measurements, Non-recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Other real estate owned	0	0
Total Assets	0	0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets	1,315,878	1,190,663
Level 2 [Member] | Fair Value, Measurements, Non-recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	57,636	82,949
Other real estate owned	11,389	11,981
Total Assets	69,025	94,930
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets	25,932	24,793
Level 3 [Member] | Fair Value, Measurements, Non-recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	7,956	6,827
Other real estate owned	215	247
Total Assets	$ 8,171	$ 7,074