Summary of Significant Accounting Policies Equity Offerings (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity Offering [Line Items]
Proceeds from issuance of common stock, net	$ 781.4	$ 0.0	$ 0.0
Share Issuance - March 2016 [Member]
Equity Offering [Line Items]
Shares Issued	37,950
Proceeds from issuance of common stock, net	$ 368.5
Share Issuance - June 2016 [Member]
Equity Offering [Line Items]
Shares Issued	23,000
Proceeds from issuance of common stock, net	$ 412.9