Debt (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Debt Instrument [Line Items]
Interest payments on debt facilities	$ 19,200,000	$ 19,300,000
Capitalized interest	100,000	$ 1,200,000
Line of Credit [Member] | Unsecured Debt [Member] | $500 Million Unsecured 2015 Line of Credit [Member]
Debt Instrument [Line Items]
Amount of line of credit	500,000,000
Net borrowings incurred	$ 45,000,000