Financing Activities (Distributions and Capital Contributions) (Details) - $ / shares	1 Months Ended	3 Months Ended
	Feb. 29, 2016	Mar. 31, 2016	Mar. 31, 2015
Distributions [Line Items]
Quarterly common stock dividend declaration date	2016-02
Dividend payable date of quarterly common stock dividend	Apr. 01, 2016
Current quarterly common stock dividend (in dollars per share)	$ 0.38	$ 0.38	$ 0.3725
Annualized current quarterly common stock dividend (in dollars per share)	$ 1.52