Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		12 Months Ended
	Jul. 31, 2015	Dec. 31, 2015	Dec. 31, 2013
Summary Of Significant Accounting Policies [Line Items]
Maturity period of highly liquid debt instruments		Three months or less
Available-for-sale securities transferred to held-to-maturity securities			$ 536,010,000
Unrealized net loss on securities reclassified from available-for-sale to held-to-maturity, Gross			$ 13,300,000
Loans past due, minimum period		90 days
Non-accrual business and commercial real estate loans		$ 250,000
Delinquency period of losses on mortgage loan to be deemed uncollectible		120 days
Allowance for loan losses		$ 0
Mortgage loans sold on real estate, final maturity period		15 years
Delinquency period of mortgage loans		90 days
Goodwill		$ 1,822,000
Colonial American Bank [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for loan losses	$ 0
Goodwill	$ 1,822,000	$ 1,800,000
Core Deposit [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization of intangible assets on accelerated basis, period		10 years
Computer Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated depreciable life of assets		3 years
Furniture, Fixtures and Other Electronic Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated depreciable life of assets		5 years
Building Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated depreciable life of assets		10 years
Buildings [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated depreciable life of assets		30 years