Debt - Summary of Interest Paid (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Debt Instrument [Line Items]
Total interest payments	$ 13.6	$ 6.3
FHLB Advance
Debt Instrument [Line Items]
Total interest payments	0.7	0.2
Convertible Senior Notes
Debt Instrument [Line Items]
Total interest payments	$ 0.0	1.8
Stated interest rate (in hundredths)	5.00%
5.75% Notes | 5.75% Notes
Debt Instrument [Line Items]
Total interest payments	$ 12.9	0.0
Stated interest rate (in hundredths)	5.75%
9% Debentures
Debt Instrument [Line Items]
Total interest payments	$ 0.0	$ 4.3
Stated interest rate (in hundredths)	9.00%