Derivatives - Classification and Fair Value of Derivatives in Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivatives
Derivative assets	$ 0.8	$ 4.1
Derivative liabilities	5.3	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	0.1	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	3.8	4.6
Foreign currency forwards | Derivatives not designated as hedging instruments
Derivatives
Notional Value	15.0
Foreign currency forwards | Derivatives not designated as hedging instruments | Other assets
Derivatives
Derivative assets	0.2
Weather derivatives | Derivatives not designated as hedging instruments
Derivatives
Notional Value	121.6	150.5
Weather derivatives | Derivatives not designated as hedging instruments | Other assets
Derivatives
Derivative assets		3.9
Weather derivatives | Derivatives not designated as hedging instruments | Other liabilities
Derivatives
Derivative liabilities	1.3
Equity futures contracts | Derivatives not designated as hedging instruments
Derivatives
Notional Value	17.0
Equity futures contracts | Derivatives not designated as hedging instruments | Other liabilities
Derivatives
Derivative liabilities	0.2
Equity put options | Derivatives not designated as hedging instruments
Derivatives
Notional Value	10.9	6.2
Equity put options | Derivatives not designated as hedging instruments | Other assets
Derivatives
Derivative assets	$ 0.5
Equity put options | Derivatives not designated as hedging instruments | Other liabilities
Derivatives
Derivative liabilities		$ 0.5