Summary of Significant Accounting Policies - Revenue Recognition Policy Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Unearned revenue		$ 77.0	$ 114.3
Deferred costs		$ 14.4	$ 34.4
Minimum [Member]
Deferred Revenue Arrangement [Line Items]
Payment terms	30 days
Maximum [Member]
Deferred Revenue Arrangement [Line Items]
Payment terms	90 days