Computation of Net Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Computation of Net Earnings per Share
Net income available to common stockholders	$ 11,841	$ 2,151	$ 35,279	$ 7,036
Weighted average common shares outstanding used in computing basic income per share	31,274	29,221	30,550	29,118
Incremental options and RSUs	2,250	1,816	2,498	1,642
Weighted average common shares used in computing diluted net income per share	33,524	31,037	33,048	30,760
Net income per share
Basic	$ 0.38	$ 0.07	$ 1.15	$ 0.24
Diluted	$ 0.35	$ 0.07	$ 1.07	$ 0.23
Weighted average number diluted shares outstanding adjustment	4	900	200	900