Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reconciliation of information used in computing basic and diluted earnings per share [Abstract]
Earnings from continuing operations	$ 130,084	$ 186,483	$ 347,730	$ 459,307
(Losses) earnings from discontinued operations, net	0	(385)	0	268,697
Net earnings	$ 130,084	$ 186,098	$ 347,730	$ 728,004
Basic earnings (loss) per common share:
Earnings from continuing operations (in dollars per basic share)	$ 0.84	$ 1.20	$ 2.24	$ 2.90
Earnings from discontinued operations, net (in dollars per basic share)	0.00	0.00	0.00	1.70
Net earnings (in dollars per basic share)	$ 0.84	$ 1.20	$ 2.24	$ 4.59
Weighted average shares outstanding - basic (in shares)	155,300,000	155,300,000	155,182,000	158,507,000
Diluted earnings (loss) per common share:
Earnings from continuing operations (in dollars per diluted share)	$ 0.83	$ 1.19	$ 2.22	$ 2.87
Earnings from discontinued operations, net (in dollars per diluted share)	0.00	0.00	0.00	1.68
Net earnings (in dollars per diluted share)	$ 0.83	$ 1.19	$ 2.22	$ 4.55
Weighted average shares outstanding - diluted (in shares)	156,798,000	156,560,000	156,562,000	160,112,000
Reconciliation Of Share Amounts Used In Computing Earnings Per Share [Abstract]
Weighted average shares outstanding - basic (in shares)	155,300,000	155,300,000	155,182,000	158,507,000
Dilutive effect of assumed exercise of employee stock options, SAR's and performance shares (in shares)	1,498,000	1,260,000	1,380,000	1,605,000
Weighted average shares outstanding - diluted (in shares)	156,798,000	156,560,000	156,562,000	160,112,000
Antidilutive securities excluded from computation of earnings per share	21,000	47,000	31,000	44,000