Net Earnings Per Share Net Earnings Per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator for earnings per share:
Net earnings for basic and diluted earnings per share	$ 52,857	$ 46,486	$ 127,509	$ 148,280
Denominator for earnings per share:
Weighted average number of common shares outstanding	141,433	141,863	141,315	142,849
Assumed exercises of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method	1,980	2,368	2,441	1,982
Weighted average diluted shares outstanding	143,413	144,231	143,756	144,831