Investments - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2015 USD ($) Funds	Jun. 30, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Number of investment funds | Funds	3
Unfunded commitments	$ 1.0
Fixed maturities and cash equivalents on deposit with various insurance departments at fair value and amortized cost	6.4
Cash equivalents on deposit with another insurance company at fair value and amortized cost	9.4
Collateralized mortgage obligations: Non-agency backed - residential
Schedule of Available-for-sale Securities [Line Items]
Non credit other than temporary impairment for securities	0.9	$ 0.9
Collateralized mortgage obligations: Non-agency backed - commercial
Schedule of Available-for-sale Securities [Line Items]
Non credit other than temporary impairment for securities	$ 0.2	$ 0.2