Net Earnings Per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator for earnings per share:
Net earnings for basic and diluted earnings per share	$ 73,072	$ 52,857	$ 171,482	$ 127,509
Denominator for earnings per share:
Weighted average number of common shares outstanding	139,596	141,433	139,808	141,315
Assumed exercises of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method	929	1,980	1,454	2,441
Weighted average diluted shares outstanding	140,525	143,413	141,262	143,756