Statutory Restrictions on Investments and Stockholders' Equity (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statutory Accounting Practices [Line Items]
Deposit invested with state treasurers	$ 127.1	$ 133.0
Dividends, loans and advances available to parent from subsidiaries	547.9
Differences in state prescribed or permitted practices to NAIC Statutory Accounting	61.7	11.7
FATICO
Statutory Accounting Practices [Line Items]
Statutory surplus maintained by insurance subsidiary	1.1	978.7
Statutory net income of insurance subsidiary	191.8	393.1	$ 199.1
Permitted accounting practice	$ 58.9	$ 8.2