Subsequent Events (Details) - Subsequent events $ / shares in Units, $ in Millions	1 Months Ended
	Apr. 30, 2018 USD ($) $ / shares
3.875% senior unsecured notes, issued in April 2018 and due in 2025
Subsequent events
Issuance of Debt	$ 500.0
Interest rate (as a percent)	3.875%
Principal amount of public offering (as a percent)	99.50%
Effective yield to maturity (as a percent)	3.957%
Net proceeds on public offering	$ 493.0
Common stock
Subsequent events
Common stock, dividends declared (in dollars per share) | $ / shares	$ 0.2195