Equity and Capital (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	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	323,353	269,929
Common stock offering, maximum aggregate price still available	$ 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