Revenue from Contracts with Customers - Contract Balances (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)
Revenue from Contracts with Customers
Signing bonuses received from vendors | item	2
Contract liabilities	$ 1.8	$ 2.6
Decrease in recognized revenues and contract liabilities	0.8	0.8
Change in contract liabilities due to changes in transaction price estimates	0.0
Receivables from contracts with customers or contract assets	$ 0.0	$ 0.0