Bradley Agreement - Additional Information (Details) - Bradley International Airport parking facilities operating agreement	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) parking_space	Sep. 30, 2017 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2002 USD ($)	Dec. 31, 2025 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Agreement period for operation of parking spaces			25 years
Number of garage parking spaces at Bradley International Airport operated | parking_space			3,500
Annual minimum guaranteed payment to the State by the trustee							$ 11,500,000
Maximum premium percentage on initial deficiency payment (not more than)			10.00%
Estimated accrued deficiency payments	$ 0		$ 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	18,500,000		$ 18,500,000				$ 17,700,000
Management fees	$ 0	$ 0	$ 0	$ 0
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Annual minimum guaranteed payment to the State by the trustee								$ 8,300,000
State of Connecticut special facility revenue bonds | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Annual principal and interest on revenue bonds								$ 3,600,000
Forecast
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Annual minimum guaranteed payment to the State by the trustee						$ 11,800,000
Forecast | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Annual minimum guaranteed payment to the State by the trustee					$ 13,200,000
Forecast | State of Connecticut special facility revenue bonds | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Annual principal and interest on revenue bonds									$ 4,500,000