Loans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Single family loans in FDIC acquired loans covered by loss share agreement	$ 196,700,000
Balances of loans due from related parties	16,200,000	61,100,000
Changes in new loans	12,900,000
Repayments in affiliates loans	12,900,000
Net balance reduction in directors and affiliates loans	(44,900,000)
Interest that would have been recorded on nonaccrual loans	3,600,000	5,400,000	7,800,000
Interest recovered on nonaccrual loans	1,500,000	3,000,000	2,600,000
Nonaccrual loans	79,537,000	99,686,000
Troubled debt restructuring	16,000,000	24,900,000
Minimum bank portfolio loan need to be reviewed	1,000,000
Loans held for sale	20,252,000	24,515,000
Troubled Debt Restructurings [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Nonaccrual loans	$ 7,000,000	$ 15,700,000
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