Shareholders' Equity - Dividends Declared (Details) - Dividend Paid - USD ($) $ / shares in Units, $ in Millions	Oct. 15, 2018	Jul. 10, 2018	Apr. 11, 2018	Feb. 05, 2018	Oct. 12, 2017	Jul. 10, 2017	Apr. 25, 2017	Feb. 06, 2017	Oct. 18, 2016	Jul. 20, 2016	Apr. 20, 2016	Feb. 03, 2016
Dividends Payable [Line Items]
Distribution Per Share (in dollars per share)	$ 0.47	$ 0.47	$ 0.47	$ 0.47	$ 0.47	$ 0.47	$ 0.47	$ 0.47	$ 0.43	$ 0.43	$ 0.43	$ 0.43
Aggregate Payment Amount	$ 57.2	$ 57.2	$ 57.4	$ 58.3	$ 58.3	$ 58.3	$ 58.4	$ 52.5	$ 48.8	$ 48.7	$ 48.7	$ 48.5
Qualified
Dividends Payable [Line Items]
Distribution Per Share (in dollars per share)	$ 0.0461171	$ 0.0461171	$ 0.0461171	$ 0.0461171	$ 0.0176751	$ 0.0176751	$ 0.0176751	$ 0.0175622	$ 0.0493613	$ 0.0493613	$ 0.0493613	$ 0.0493613
Non-Qualified
Dividends Payable [Line Items]
Distribution Per Share (in dollars per share)	0.2090220	0.2090220	0.2090220	0.2090220	0.2484259	0.2484259	0.2484259	0.2468402	0.2886402	0.2886402	0.2886402	0.2886402
Nondividend Distributions
Dividends Payable [Line Items]
Distribution Per Share (in dollars per share)	$ 0.2148609	$ 0.2148609	$ 0.2148609	$ 0.2148609	$ 0.2038990	$ 0.2038990	$ 0.2038990	$ 0.2025975	$ 0.0953319	$ 0.0953319	$ 0.0953319	$ 0.0953319