Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Earnings from continuing operations (in dollars per diluted share)	$ 1.05	$ 1.01	$ 2.82	$ 2.90
Earnings (loss) per share from discontinued operations (in dollars per diluted share)	$ 0.00	$ 0.12	$ (0.03)	$ 0.37
Earnings from continuing operations	$ 157,305	$ 159,455	$ 433,170	$ 457,018
Earnings (loss) from discontinued operations	0	19,457	(4,472)	58,199
Reconciliation of information used in computing basic and diluted earnings per share [Abstract]
Net earnings	$ 157,305	$ 178,912	$ 428,698	$ 515,217
Basic earnings (loss) per common share:
Net earnings (in dollars per basic share)	$ 1.07	$ 1.15	$ 2.84	$ 3.31
Weighted average shares outstanding - basic (in shares)	147,344,000	155,757,000	151,177,000	155,668,000
Diluted earnings (loss) per common share:
Net earnings (in dollars per diluted share)	$ 1.05	$ 1.14	$ 2.79	$ 3.27
Weighted average shares outstanding - diluted (in shares)	149,457,000	157,555,000	153,429,000	157,565,000
Reconciliation Of Share Amounts Used In Computing Earnings Per Share [Abstract]
Weighted average shares outstanding - basic (in shares)	147,344,000	155,757,000	151,177,000	155,668,000
Dilutive effect of assumed exercise of SAR's and vesting of performance shares (in shares)	2,113,000	1,798,000	2,252,000	1,897,000
Weighted average shares outstanding - diluted (in shares)	149,457,000	157,555,000	153,429,000	157,565,000
Antidilutive securities excluded from computation of earnings per share	10,000	87,000	1,000	37,000
Earnings from continuing operations (in dollars per basic share)	$ 1.07	$ 1.02	$ 2.87	$ 2.94
Earnings (loss) per share from discontinued operations (in dollars per basic share)	$ 0.00	$ 0.12	$ (0.03)	$ 0.37