Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
BASIC
Weighted average number of common shares outstanding used in computing basic earnings per share	48,076	46,889	47,872	46,794
Net income attributable to common stockholders	$ 15,078	$ 17,385	$ 26,210	$ 27,587
Earnings per share attributable to common stockholders	$ 0.31	$ 0.37	$ 0.55	$ 0.59
DILUTED
Weighted average number of common shares outstanding used in computing basic earnings per share	48,076	46,889	47,872	46,794
Add: Dilutive effect of stock options and stock awards outstanding	1,174	1,534	1,219	1,429
Diluted shares	49,250	48,423	49,091	48,223
Net income attributable to common stockholders	$ 15,078	$ 17,385	$ 26,210	$ 27,587
Earnings per share attributable to common stockholders	$ 0.31	$ 0.36	$ 0.53	$ 0.57