Loans and Allowance for Loan Losses - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Interest that would have been recorded on nonaccrual loans	$ 1,800,000
Interest recorded on nonaccrual loans	600,000
Nonaccrual loans	118,445,000	$ 79,537,000
Troubled debt restructuring both accruing and nonaccruing	12,800,000	16,000,000
Minimum bank portfolio loan need to be reviewed	1,000,000
Real estate acquired through foreclosure	37,371,000	58,415,000
Consumer [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Nonaccrual loans	4,855,000	5,748,000
Mortgage loan in process of foreclosure	7,000,000	13,700,000
Real estate acquired through foreclosure	$ 9,900,000	12,700,000
Performing [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Period for which payments of principal and interest are past due	Less than 90 days
Troubled Debt Restructurings [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Nonaccrual loans	$ 4,900,000	7,000,000
FDIC Acquired Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Nonaccrual loans	1,589,000	2,102,000
FDIC Acquired Loans [Member] | Consumer [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Nonaccrual loans		174,000
Mortgage loan in process of foreclosure	6,200,000	8,100,000
Real estate acquired through foreclosure	$ 4,200,000	$ 8,200,000