Net Earnings Per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator for earnings per share:
Net earnings for basic and diluted earnings per share	$ 58,633	$ 73,072	$ 105,126	$ 171,482
Denominator for earnings per share:
Weighted average number of common shares outstanding	136,963	139,596	137,438	139,808
Assumed exercises of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method	975	929	1,156	1,454
Weighted average diluted shares outstanding	137,938	140,525	138,594	141,262