Insurance Subsidiary - Financial Information Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014	Apr. 06, 2011
Statutory Accounting Practices [Line Items]
Dividends Declared But Not Paid	$ 123.9
Payments of Dividends	123.9
Statutory Accounting Practices, Statutory Capital and Surplus, Unassigned Balance Netted Against Additional Paid in Capital					$ 805.8
Statutory Accounting Practices, Statutory Capital and Surplus, Increase (Decrease) as a Result of ReDomestication by Entity			$ 4.1	$ 17.3
Statutory Accounting Practices, Non-Permitted Practice, Change in Statutory Capital and Surplus			(13.7)	(75.1)
IOWA
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Permitted Practice, Change in Statutory Capital and Surplus			46.8	(5.0)
Raven Re [Member]
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices Statutory Capital And Surplus Change			220.0	245.0
Statutory Accounting Practices, Statutory Capital and Surplus, Balance			$ 210.3	$ 187.3
Non Agency Residential Mortgage Backed Securities [Member]
Statutory Accounting Practices [Line Items]
Other Marketable Securities, Current	$ 16,012.3	$ 18,074.6