Long-term Debt - Convertible Senior Notes (Additional Notes) (Details) $ / shares in Units, shares in Millions, $ in Millions	Sep. 11, 2018 USD ($) $ / shares shares	Jun. 30, 2020 $ / shares
Debt Instrument [Line Items]
Maturity date		Sep. 15, 2023
Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Net proceeds to repurchase common stock	$ 38.8
Purchases of treasury stock and buyback of shares for taxes (in shares) | shares	1.3
Cost of hedging transactions	$ 8.6
Convertible Debt | Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Interest rate stated, percentage		2.375%
Aggregated principal amount	143.8
Initial purchasers' discount and issuance costs	(4.4)
Proceeds from debt, net of issuance costs	$ 139.4
Shares conversion rate	26.5957
Initial conversion price (in dollars per share) | $ / shares	$ 37.60	$ 35.78
Initial liability component of note	$ 122.9
Debt borrowing rate, percentage	5.70%
Debt discount for conversion option	$ 20.9
Deferred tax effect on conversion	5.4
Deferred financing cost	4.8
Deferred finance cost, attributable liability component	4.1
Deferred finance costs, equity component	0.7
Deferred tax asset, convertible debt equity component	0.2
Revolving Credit Facility | Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Net proceeds to pay down revolving credit facility	$ 49.0