Investments - Additional Information (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) Fund	Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Number of investment funds | Fund	3
Withdrawal from the limited partnership investments	$ 2.3
Unfunded commitments	0.9
Fixed maturities and cash equivalents on deposit with various insurance departments at fair value and amortized cost	6.6
Cash equivalents on deposit with another insurance company at fair value and amortized cost	9.7
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