Computation of Net Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Computation of Net Earnings per Share
Net income available to common stockholders	$ 8,838	$ 11,841	$ 37,422	$ 35,279
Weighted average common shares outstanding used in computing basic income per share	32,365	31,274	32,225	30,550
Incremental options and RSUs	1,608	2,250	1,807	2,498
Weighted average common shares used in computing diluted net income per share	33,973	33,524	34,032	33,048
Net income per share
Basic	$ 0.27	$ 0.38	$ 1.16	$ 1.15
Diluted	$ 0.26	$ 0.35	$ 1.10	$ 1.07
Weighted average number diluted shares outstanding adjustment	300	4	11	200