Bradley Agreement - Schedule of Interest and Premium Received and Deficiency Payments (Details) - Bradley International Airport parking facilities operating agreement - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Loss Contingencies [Line Items]
Deficiency repayments	$ 0.4	$ 0.9	$ 2.8	$ 2.9
Interest	0.3	0.0	0.8	0.5
Premium	$ 0.0	$ 0.1	$ 0.3	$ 0.2