Shareholders' Equity - Dividends declared (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2016	Jul. 20, 2016	Apr. 20, 2016	Feb. 03, 2016	Nov. 03, 2015	Jul. 31, 2015	Apr. 29, 2015	Feb. 06, 2015
Dividends declared/paid [Abstract]
Minimum percentage of taxable income to be distributed as REIT	90.00%
Distribution Per Share (USD per share)		$ 0.65	$ 0.65	$ 0.65	$ 0.65	$ 0.62	$ 0.62	$ 0.62
Aggregate Payment Amount		$ 48.7	$ 48.7	$ 48.5	$ 48.5	$ 46.3	$ 46.3	$ 46.0