Investments - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) Funds	Sep. 30, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Number of investment funds | Funds	3
Unfunded commitments	$ 0.5
Incremental percentage of withdrawal of other investments	25.00%
Fixed maturities and cash equivalents on deposit with various insurance departments at fair value and amortized cost	$ 6.3
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