Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Earnings from continuing operations (in dollars per diluted share)	$ 1.08	$ 0.90	$ 1.77	$ 1.89
(Loss) earnings per share from discontinued operations (in dollars per diluted share)	$ (0.17)	$ 0.14	$ (0.03)	$ 0.25
Earnings from continuing operations	$ 166,456	$ 142,475	$ 275,865	$ 297,563
(Loss) earnings from discontinued operations	(26,497)	21,583	(4,472)	38,742
Reconciliation of information used in computing basic and diluted earnings per share [Abstract]
Net earnings	$ 139,959	$ 164,058	$ 271,393	$ 336,305
Basic earnings (loss) per common share:
Net earnings (in dollars per basic share)	$ 0.92	$ 1.05	$ 1.77	$ 2.16
Weighted average shares outstanding - basic (in shares)	151,744,000	155,703,000	153,124,000	155,622,000
Diluted earnings (loss) per common share:
Net earnings (in dollars per diluted share)	$ 0.91	$ 1.04	$ 1.74	$ 2.14
Weighted average shares outstanding - diluted (in shares)	153,938,000	157,513,000	155,573,000	157,457,000
Reconciliation Of Share Amounts Used In Computing Earnings Per Share [Abstract]
Weighted average shares outstanding - basic (in shares)	151,744,000	155,703,000	153,124,000	155,622,000
Dilutive effect of assumed exercise of SAR's and vesting of performance shares (in shares)	2,194,000	1,810,000	2,449,000	1,835,000
Weighted average shares outstanding - diluted (in shares)	153,938,000	157,513,000	155,573,000	157,457,000
Antidilutive securities excluded from computation of earnings per share	78,000	33,000	0	20,000
Earnings from continuing operations (in dollars per basic share)	$ 1.10	$ 0.92	$ 1.80	$ 1.91
(Loss) earnings per share from discontinued operations (in dollars per basic share)	$ (0.17)	$ 0.14	$ (0.03)	$ 0.25