Bradley Agreement - Schedule of Interest and Premium Received and Deficiency Payment (Details) - Bradley International Airport parking facilities operating agreement - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deficiency repayments	$ 1.7	$ 1.8	$ 1.3
Interest	0.5	0.4	0.5
Premium	$ 0.2	$ 0.2	$ 0.1

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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