Equity-Based Plans (Details) - USD ($)	3 Months Ended			12 Months Ended
	Jun. 30, 2015	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
stock offering	10,400,000		11,100,000		700,000
Proceeds from Issuance of Common Stock		$ 20,000,000	$ 47,000,000	$ 271,000,000	$ 0	$ 67,000,000
employee stock purchase plan shares authorized				625,000
Employee Stock Purchase Plan, Base Pay Threshold				10.00%
Employee Stock Purchase Plan, Purchased Stock Value Limitation				$ 25,000
Employee Stock Purchase Plan, Share Purchase Limitation				1,500
Employee Stock Purchase Plan, Purchase Price				95.00%
Employee Stock Purchase Plan, Number of Available Shares				397,265
Dividend Reinvestment and Direct Stock Purchase Plan Shares				2,500,000
Dividend Reinvestment and Direct Stock Purchase Plan, Number of Available Shares				2,478,086
Common Stock [Member]
Stock Issued During Period, Shares, New Issues			1,665,000	10,400,000		2,365,000