Summary of Significant Accounting Policies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Sep. 11, 2018
Goodwill and Intangible Assets [Abstract]
Goodwill, Impairment Loss	$ 0	$ 0	$ 0
Minimum
Revenue from Contract with Customer [Abstract]
Period of cancellation notice	10 days
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment, Useful Life	1 year
Goodwill and Intangible Assets [Abstract]
Finite-Lived Intangible Asset, Useful Life	1 year
Maximum
Revenue from Contract with Customer [Abstract]
Period of cancellation notice	30 days
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment, Useful Life	7 years
Goodwill and Intangible Assets [Abstract]
Finite-Lived Intangible Asset, Useful Life	10 years
Accounting Standards Update 2016-02 | Scenario, Forecast
Goodwill and Intangible Assets [Abstract]
ROU asset				$ 22,000,000
Operating lease liability				$ 23,000,000
Convertible Debt | Convertible Senior Notes Due 2023
Property, Plant and Equipment [Line Items]
Percent rate stated, percentage	2.375%				2.375%