Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
BASIC
Weighted average number of common shares outstanding used in computing basic earnings per share	46,889	46,148	46,794	46,085
Net income attributable to common stockholders	$ 17,385	$ 8,635	$ 27,587	$ 6,709
Earnings per share attributable to common stockholders	$ 0.37	$ 0.19	$ 0.59	$ 0.15
DILUTED
Weighted average number of common shares outstanding used in computing basic earnings per share	46,889	46,148	46,794	46,085
Add: Dilutive effect of stock options and stock awards outstanding	1,534	1,359	1,429	1,298
Diluted shares	48,423	47,507	48,223	47,383
Net income attributable to common stockholders	$ 17,385	$ 8,635	$ 27,587	$ 6,709
Earnings per share attributable to common stockholders	$ 0.36	$ 0.18	$ 0.57	$ 0.14