Equity and Capital (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Jul. 31, 2015	Mar. 01, 2013
Targeted or Tracking Stock, Stock [Line Items]
Common stock offering, maximum aggregate price					$ 300,000,000
Commission to sales agent, maximum (percent)					2.00%
Number of shares settled		275,359	243,648
Common stock offering, maximum aggregate price still available	$ 88,507,000	$ 88,507,000
Stock repurchase program, authorized amount (in shares)				$ 200,000,000
Number of shares repurchased	0
At The Market Stock Sales
Targeted or Tracking Stock, Stock [Line Items]
Number of shares settled		8,419,298.000
Weighted-average sales price (in usd per share)		$ 25.12