Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2012 Debt Securities Mortgage and asset backed securities CMBS		Jan. 02, 2012 Debt Securities U.S. Government obligations
Fair Value, Measurement Inputs, Disclosure [Line Items]
Gross transfers out of Level 2 into Level 3	$ 41.9	[1]	$ 41.9	[1]
Gross transfers out of Level 1 into Level 2					$ 267.8

[1] Principally due to a decrease in observable inputs related to the valuation of such securities.