Cash Equivalent and Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Schedule Of Investments [Line Items]
Available For Sale Securities	$ 47.3		48.0
Certificates Of Deposit Member
Schedule Of Investments [Line Items]
Available For Sale Securities	1,217.2		842.5
fixed maturity and mutual funds [Member]
Schedule Of Investments [Line Items]
Available For Sale Securities	47.3		48.0
Proceeds From Sale Of Available For Sale Securities	$ 0.8
Minimum [Member] | fixed maturity and mutual funds [Member]
Schedule Of Investments [Line Items]
Securities Maturity period		1 month	2 months
Minimum [Member] | Short Term Investments Member
Schedule Of Investments [Line Items]
Securities Maturity period		1 month	1 month
Maximum [Member] | Certificates Of Deposit Member
Schedule Of Investments [Line Items]
Securities Maturity period		90 days
Maximum [Member] | fixed maturity and mutual funds [Member]
Schedule Of Investments [Line Items]
Securities Maturity period		20 months	23 months
Maximum [Member] | Short Term Investments Member
Schedule Of Investments [Line Items]
Securities Maturity period		8 months	10 months