Bradley Agreement - Deficiency Payments, Net of Payments Made (Details) - Bradley International Airport parking facilities operating agreement - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deficiency repayments	$ 0.0	$ 0.2	$ 1.2	$ 1.0
Interest	0.2	0.1	0.3	0.3
Premiums	$ 0.0	$ 0.0	$ 0.2	$ 0.1