Credit Quality Assessment (Additional Information) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restructured accruing	$ 1.6	$ 3.4
Mortgage Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned	2.8
Other Real Estate Owned Foreclosed Assets in Process	0.9
Restructured Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Specific allowance	0.1	0.3
Restructured accruing	5.5	9.5
Restructured non-accruing	6.1	10.5
Financing Receivable Troubled Debt Restructurings Restructured Total	11.6	20.0
Other real estate owned	3.2	1.3
Additional Financing Receivable Troubled Debt Restructurings Restructured	$ 0.1	$ 5.5