Net Earnings Per Share Net Earnings Per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator for earnings per share:
Net earnings for basic and diluted earnings per share	$ 44,758	$ 50,158	$ 74,652	$ 101,794
Denominator for earnings per share:
Weighted average number of common shares outstanding	141,574	142,085	141,255	143,350
Assumed exercises of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method	2,546	1,689	2,709	1,631
Weighted average diluted shares outstanding	144,120	143,774	143,964	144,981