Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates	$ 0.0		$ 8.1
Goodwill	31.7	$ 24.1	24.1	$ 31.7	$ 24.1
Intangible Assets, Net (Excluding Goodwill)	$ 21.3	32.2	32.2	$ 24.2	$ 31.3
LowFares.com
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates		$ 3.9	$ 3.9