Net Earnings Per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator for earnings per share:
Net earnings for basic and diluted earnings per share	$ 45,368	$ 50,500	$ 46,493	$ 98,410
Denominator for earnings per share:
Weighted average number of common shares outstanding	137,861	140,063	137,686	139,916
Assumed exercises of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method	1,132	1,428	1,146	1,568
Weighted average diluted shares outstanding	138,993	141,491	138,832	141,484