Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings from continuing operations	$ 206,006	$ 157,305	$ 509,796	$ 433,170
Loss from discontinued operations	0	0	0	(4,472)
Net earnings	$ 206,006	$ 157,305	$ 509,796	$ 428,698
Basic earnings (loss) per common share:
Earnings from continuing operations (in dollars per basic share)	$ 1.42	$ 1.07	$ 3.51	$ 2.87
Earnings (loss) per share from discontinued operations (in dollars per basic share)	0	0	0	(0.03)
Net earnings (in dollars per basic share)	$ 1.42	$ 1.07	$ 3.51	$ 2.84
Weighted average shares outstanding - basic (in shares)	145,372,000	147,344,000	145,276,000	151,177,000
Diluted earnings (loss) per common share:
Earnings from continuing operations (in dollars per diluted share)	$ 1.40	$ 1.05	$ 3.47	$ 2.82
Earnings (loss) per share from discontinued operations (in dollars per diluted share)	0	0	0	(0.03)
Net earnings (in dollars per diluted share)	$ 1.40	$ 1.05	$ 3.47	$ 2.79
Weighted average shares outstanding - diluted (in shares)	147,051,000	149,457,000	147,053,000	153,429,000
Reconciliation Of Share Amounts Used In Computing Earnings Per Share [Abstract]
Weighted average shares outstanding - basic (in shares)	145,372,000	147,344,000	145,276,000	151,177,000
Dilutive effect of assumed exercise of SAR's and vesting of performance shares (in shares)	1,679,000	2,113,000	1,777,000	2,252,000
Weighted average shares outstanding - diluted (in shares)	147,051,000	149,457,000	147,053,000	153,429,000
Antidilutive securities excluded from computation of earnings per share	28,000	10,000	9,000	1,000