Debt - Cash Convertible Senior Notes Due 2019 (Details) - USD ($) $ in Millions	1 Months Ended
	Jul. 31, 2017	Jul. 31, 2014	Jun. 30, 2014	Sep. 30, 2019	Jun. 15, 2019
2.125% Cash Convertible Senior Notes Due 2019
Debt Instrument [Line Items]
Stated interest rate			2.125%	2.125%
Convertible senior notes issued and settled		$ 30.0	$ 200.0
Amount of retired debt	$ 35.0
Repurchased amount					$ 195.0
2024 Convertible Notes
Debt Instrument [Line Items]
Stated interest rate	2.875%
Convertible senior notes issued and settled	$ 34.4