Reserves for Unpaid Losses and Loss Adjustment Expenses (Incurred Loss and Allocated LAE, Net of Reinsurance - Specialty Products - Other) (Details) - Other - Specialty Products $ in Millions	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)	Dec. 31, 2007 USD ($)
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 478.0
2007
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims	5,073
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 28.6	$ 28.6	$ 28.6	$ 28.6	$ 28.6	$ 28.6	$ 28.6	$ 26.8	$ 26.7	$ 26.8
2008
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims	5,192
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 31.2	31.2	31.2	31.2	31.2	31.2	31.2	31.5	$ 31.7
2009
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims	5,138
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 30.9	30.9	30.9	30.9	30.8	31.3	31.4	$ 33.8
2010
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims	5,182
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 32.5	32.5	32.5	32.6	32.5	34.3	$ 34.7
2011
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims	5,306
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 35.4	35.4	35.4	35.4	35.5	$ 33.2
2012
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims	5,324
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 37.0	36.9	36.9	36.9	$ 36.6
2013
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims	5,510
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 39.2	39.2	40.6	$ 39.6
2014
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims	9,971
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 92.9	90.8	$ 96.6
2015
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 1.8
Cumulative number of reported claims	10,704
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 73.2	$ 75.5
2016
Claims Development [Line Items]
Total IBNR plus expected development on reported claims	$ 33.8
Cumulative number of reported claims	4,306
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 77.1