Summary of Significant Accounting Policies - Sales and Marketing (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Marketing and advertising expenses	$ 70.7	$ 79.6	$ 58.1
Prepaid media costs	1.6	1.8
Accrued marketing and advertising expenses	$ 2.1	$ 2.0