Net Investment Income (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
|
Schedule of Investment Income, Reported Amounts, by Category [Line Items] | ||||
Investment income | $ 19.3 | $ 18.7 | $ 58.0 | $ 56.4 |
Investment expenses | 0.8 | 0.8 | 2.6 | 2.3 |
Net investment income | 18.5 | 17.9 | 55.4 | 54.1 |
Debt Securities [Member] | ||||
Schedule of Investment Income, Reported Amounts, by Category [Line Items] | ||||
Investment income related to fixed maturity securities and short-term investments and cash equivalents | 17.4 | 16.9 | 52.4 | 50.8 |
Equity Securities [Member] | ||||
Schedule of Investment Income, Reported Amounts, by Category [Line Items] | ||||
Investment income related to equity securities | 1.7 | 1.7 | 5.2 | 5.4 |
Short-term Investments [Member] | ||||
Schedule of Investment Income, Reported Amounts, by Category [Line Items] | ||||
Investment income related to fixed maturity securities and short-term investments and cash equivalents | $ 0.2 | $ 0.1 | $ 0.4 | $ 0.2 |