Derivatives - Classification and Fair Value of Derivatives in Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivatives
Derivative assets	$ 2.9	$ 4.1
Derivative liabilities	6.0	5.1
Interest rate cap | Derivatives not designated as hedging instruments
Derivatives
Notional Value	250.0	250.0
Interest rate cap | Derivatives not designated as hedging instruments | Other assets
Derivatives
Derivative assets		0.2
Foreign currency swaps | Derivatives not designated as hedging instruments
Derivatives
Notional Value	90.0	45.0
Foreign currency swaps | Derivatives not designated as hedging instruments | Other liabilities
Derivatives
Derivative liabilities	4.9	4.6
Foreign currency forwards | Derivatives not designated as hedging instruments
Derivatives
Notional Value	10.0
Foreign currency forwards | Derivatives not designated as hedging instruments | Other liabilities
Derivatives
Derivative liabilities	0.8
Weather derivatives | Derivatives not designated as hedging instruments
Derivatives
Notional Value	53.4	150.5
Weather derivatives | Derivatives not designated as hedging instruments | Other assets
Derivatives
Derivative assets	1.7	3.9
Equity futures contracts | Derivatives not designated as hedging instruments
Derivatives
Notional Value	8.1
Equity put options | Derivatives not designated as hedging instruments
Derivatives
Notional Value	14.7	6.2
Equity put options | Derivatives not designated as hedging instruments | Other assets
Derivatives
Derivative assets	0.8
Equity put options | Derivatives not designated as hedging instruments | Other liabilities
Derivatives
Derivative liabilities	0.3	$ 0.5
Equity warrants | Derivatives not designated as hedging instruments
Derivatives
Notional Value	0.4
Equity warrants | Derivatives not designated as hedging instruments | Other assets
Derivatives
Derivative assets	$ 0.4