Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Schedule of Investments [Line Items]
Increase (decrease) in OTTI losses within OCI	$ 0.1	$ (0.9)	$ (0.3)	$ (1.9)
Equity Securities
Schedule of Investments [Line Items]
Percentage of fair value over cost	80.00%		80.00%