Shareholders' Equity - Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2017	Jul. 10, 2017	Apr. 25, 2017	Feb. 06, 2017	Oct. 18, 2016	Jul. 20, 2016	Apr. 20, 2016	Feb. 03, 2016
Equity [Abstract]
Minimum percentage of taxable income to be distributed as REIT	90.00%
Distribution Per Share (USD per share)		$ 0.47	$ 0.47	$ 0.47	$ 0.43	$ 0.43	$ 0.43	$ 0.43
Aggregate Payment Amount		$ 58.3	$ 58.4	$ 52.5	$ 48.8	$ 48.7	$ 48.7	$ 48.5