Bradley Agreement - Narrative (Details) - Bradley International Airport parking facilities operating agreement - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Agreement period for operation of parking spaces	25 years
Maximum premium percentage on initial deficiency payment (not to exceed)	10.00%
Estimated accrued deficiency payments	$ 0		$ 0
Management fee apportioned to the entity (as a percent)	60.00%
Management fee apportioned to an un-affiliated entity (as a percent)	40.00%
Unrecognized cumulative management fees	$ 19,900,000		$ 19,700,000
Management fees	$ 0	$ 0