Net Earnings Per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator for earnings per share:
Net earnings for basic and diluted earnings per share	$ 50,500	$ 44,758	$ 98,410	$ 74,652
Denominator for earnings per share:
Weighted average number of common shares outstanding	140,063	141,574	139,916	141,255
Assumed exercises of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method	1,428	2,546	1,568	2,709
Weighted average diluted shares outstanding	141,491	144,120	141,484	143,964