Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Number of investment funds	3
Unfunded commitments	$ 2.3
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] | Collateralized Non Agency Backed Residential Obligations
Schedule of Available-for-sale Securities [Line Items]
Non credit other than temporary impairment for securities	0.9	0.9
Collateralized Mortgage Obligations [Member] | Collateralized Non Agency Backed Commercial Obligations
Schedule of Available-for-sale Securities [Line Items]
Non credit other than temporary impairment for securities	$ 0.2	$ 0.2