Equity - Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity
Dividend amount for current period (in dollars per share)	$ 3.60	$ 3.40	$ 3.20
Aggregated dividend paid	$ 188.3	$ 174.5	$ 163.7
Minimum percentage of adjusted funds from operations as cash dividend (as a percent)	50.00%
Percentage of REIT taxable income as cash dividend (as a percent)	100.00%