Computation of Net Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Computation of Net Earnings per Share
Net income available to common stockholders	$ 13,915	$ 9,506
Weighted average common shares outstanding used in computing basic income per share	32,094	29,772
Incremental options and RSUs	2,029	2,483
Weighted average common shares used in computing diluted net income per share	34,123	32,255
Net income per share
Basic	$ 0.43	$ 0.32
Diluted	$ 0.41	$ 0.29
Weighted average number diluted shares outstanding adjustment	10	100