Loans and Allowance for Loan Losses - Schedule of Credit Quality Indicators of Various Classes of Loans - Credit Risk Profile Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 1,578,583	$ 1,654,170
Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,571,594	1,645,199
Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	6,989	8,971
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,387,243	1,351,776
Originated loans [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,382,144	1,345,487
Originated loans [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	5,099	6,289
Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	130,649	202,974
Acquired [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	128,759	200,292
Acquired [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,890	2,682
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	60,691	99,420
Covered loans [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 60,691	$ 99,420