Bradley Agreement - Schedule of Interest and Premium Received and Deficiency Payments (Details) - Bradley International Airport Parking Facilities Operating Agreement - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Deficiency repayments	$ 0.1	$ 3.8	$ 3.9
Interest	$ 0.1	1.0	0.9
Premium		$ 0.4	$ 0.3

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