Derivatives - Interest Rate Cap (Details) - Interest rate cap $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) item
Derivatives
Number of financial institutions entered into derivative contracts | item	2
Derivatives not designated as hedging instruments
Derivatives
Collateral balances held	$ 0.2
Barclays Bank Plc | Derivatives not designated as hedging instruments | A
Derivatives
Collateral balances held	0.1
Nordea Bank Abp | Derivatives not designated as hedging instruments | AA-
Derivatives
Collateral balances held	$ 0.1