Loans and Allowance for Loan Losses - Schedule of Credit Quality Indicators of Various Classes of Loans - Credit Risk Profile Based on Payment Activity (Detail) (Construction Credit Exposure [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	$ 1,113,510	$ 1,106,761
Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,087,449	1,073,964
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	14,579	21,123
FDIC Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	11,482	11,674
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,040,029	1,028,973
Pass [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,032,054	1,012,128
Pass [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	5,225	14,377
Pass [Member] | FDIC Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	2,750	2,468
Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	21,754	22,480
Pass-Watch [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	18,493	21,516
Pass-Watch [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	2,727	432
Pass-Watch [Member] | FDIC Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	534	532
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	9,554	7,545
Special Mention [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	9,100	7,097
Special Mention [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	139	129
Special Mention [Member] | FDIC Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	315	319
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	42,173	47,763
Substandard [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	27,802	33,223
Substandard [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	6,488	6,185
Substandard [Member] | FDIC Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	$ 7,883	$ 8,355