Equity - Share Repurchase Plan, Preferred Stock (Details) $ / shares in Units, $ in Millions		12 Months Ended
	Oct. 23, 2018 shares	Dec. 31, 2019 USD ($) item $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Share Repurchase Plan
Increase in authorized number of shares to be repurchased	5,000,000.0
Repurchase of common shares (in shares)		600,000	6,100,000	300,000
Average costs per share | $ / shares		$ 84.33	$ 79.94	$ 74.27
Value of shares repurchased | $		$ 50.0	$ 484.9	$ 25.0
Remaining number of common stock authorized for repurchase under stock repurchase program (in shares)		6,400,000
Percent of outstanding stock authorized for repurchase		10.00%
Preferred Stock
Preferred stock, authorized shares		5,000,000	5,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.001	$ 0.001
Preferred stock, issued shares		0	0
Preferred stock, outstanding shares		0	0
Minimum number of series in which preferred shares may be issued | item		1