Computation of Net Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Computation of Net Earnings per Share
Net income available to common stockholders	$ 14,669	$ 13,932	$ 28,584	$ 23,438
Weighted average common shares outstanding used in computing basic income per share	32,214	30,589	32,154	30,183
Incremental options and RSUs	1,728	2,579	1,894	2,596
Weighted average common shares used in computing diluted net income per share	33,942	33,168	34,048	32,779
Net income per share
Basic	$ 0.46	$ 0.46	$ 0.89	$ 0.78
Diluted	$ 0.43	$ 0.42	$ 0.84	$ 0.72
Weighted average number diluted shares outstanding adjustment	300	6	10	300