Equity and Accumulated Other Comprehensive Loss, Net (Equity Distribution Agreements Narrative) (Details) - 2011 Equity Distribution Agreements - USD ($) $ / shares in Units, shares in Millions	66 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Jun. 29, 2011
Class of Stock [Line Items]
Aggregate offering price of the distribution agreement maximum			$ 400,000,000
Net proceeds from sale of common stock	$ 342,700,000
Issuance of common shares (in shares)	5.7
Equity distribution agreements at an average price per share (in dollars per share)	$ 60.35
Payment of commissions to sales agents	$ 3,500,000
Aggregate offering price remaining available for offer and sale		$ 53,800,000