Equity (Details) - shares	12 Months Ended
	Dec. 31, 2017	Apr. 26, 2017	Apr. 25, 2017	Dec. 31, 2016	Jul. 19, 2016	Jul. 18, 2016	Apr. 20, 2015	Apr. 20, 2009	Jan. 31, 2008
Class of Stock [Line Items]
Preferred stock, shares authorized	2,000,000			2,000,000			2,000,000	200,000
Preferred stock, shares issued	0			0
Preferred stock, shares outstanding	0
Common sock, shares authorized	135,000,000	135,000,000	100,000,000	100,000,000	100,000,000	60,000,000
Common Stock
Class of Stock [Line Items]
Stock repurchased during the period	0
Number of remaining shares authorized to be repurchased	500,000
Common Stock
Class of Stock [Line Items]
Number of shares authorized to be repurchased									500,000