Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities and cash equivalents on deposit with various insurance departments at fair value and amortized cost	$ 5.3
Cash equivalents on deposit with another insurance company at fair value and amortized cost	9.4
Collateralized Mortgage Obligations [Member] | Non-Agency Backed - Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Non credit other than temporary impairment for securities	1.0	1.0
Collateralized Mortgage Obligations [Member] | Non-Agency Backed - Commercial [Member]
Schedule of Available-for-sale Securities [Line Items]
Non credit other than temporary impairment for securities	$ 0.2	$ 0.2