Earnings per Share Earnings per Share (Tables)

3 Months Ended

Mar. 31, 2018

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 stock units and options to purchase common stock for the three months ended March 31, 2018 and 2017:

	Three months ended March 31,
	2018	2017
Weighted average common shares—basic	45,779,966	45,570,495
Dilutive effect of restricted stock units	358,583	283,839
Dilutive effect of stock options	90,788	54,624
Weighted average common shares—diluted	46,229,337	45,908,958