Common Stock (Details)	1 Months Ended	12 Months Ended
	Aug. 31, 2012 agreement	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Number of sales agency agreements	2
Common stock, shares authorized		200,000,000	200,000,000
Preferred stock, shares authorized		10,000,000
Preferred stock, shares outstanding		0	0
Sales Agency Agreement [Member]
Class of Stock [Line Items]
Common stock, shares authorized	2,726,390
Remaining authorized repurchase amount		1,795,199
Shares issued under sales agency agreement		0	0	931,191