Earnings per Share Earnings per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]

Schedule of Weighted Average Number of Shares [Table Text Block]

The following table summarizes the dilutive effect of restricted shares and options to purchase common stock:

	Year ended December 31,
	2017	2016	2015
Weighted average common shares—basic	45,682,627	45,407,316	45,123,626
Dilutive effect of restricted share awards	241,974	—	—
Dilutive effect of stock options	65,651	—	—
Weighted average common shares—diluted	45,990,252	45,407,316	45,123,626