Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Earnings from continuing operations	$ 198,085	$ 166,456	$ 303,790	$ 275,865
Loss from discontinued operations	0	(26,497)	0	(4,472)
Net earnings	$ 198,085	$ 139,959	$ 303,790	$ 271,393
Basic earnings (loss) per common share:
Earnings from continuing operations (in dollars per basic share)	$ 1.36	$ 1.10	$ 2.09	$ 1.80
Earnings (loss) per share from discontinued operations (in dollars per basic share)	0	(0.17)	0	(0.03)
Net earnings (in dollars per basic share)	$ 1.36	$ 0.92	$ 2.09	$ 1.77
Weighted average shares outstanding - basic (in shares)	145,366,000	151,744,000	145,227,000	153,124,000
Diluted earnings (loss) per common share:
Earnings from continuing operations (in dollars per diluted share)	$ 1.35	$ 1.08	$ 2.07	$ 1.77
Earnings (loss) per share from discontinued operations (in dollars per diluted share)	0	(0.17)	0	(0.03)
Net earnings (in dollars per diluted share)	$ 1.35	$ 0.91	$ 2.07	$ 1.74
Weighted average shares outstanding - diluted (in shares)	147,179,000	153,938,000	147,041,000	155,573,000
Reconciliation Of Share Amounts Used In Computing Earnings Per Share [Abstract]
Weighted average shares outstanding - basic (in shares)	145,366,000	151,744,000	145,227,000	153,124,000
Dilutive effect of assumed exercise of SAR's and vesting of performance shares (in shares)	1,813,000	2,194,000	1,814,000	2,449,000
Weighted average shares outstanding - diluted (in shares)	147,179,000	153,938,000	147,041,000	155,573,000
Antidilutive securities excluded from computation of earnings per share	30,000	78,000	1,200	0