Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reconciliation of information used in computing basic and diluted earnings per share [Abstract]
Net earnings	$ 226,153	$ 232,769
Basic earnings per common share:
Net earnings (in dollars per basic share)	$ 1.57	$ 1.62
Weighted average shares outstanding - basic (in shares)	144,087,000	143,765,000
Diluted earnings per common share:
Net earnings (in dollars per diluted share)	$ 1.56	$ 1.61
Weighted average shares outstanding - diluted (in shares)	145,329,000	144,938,000
Reconciliation Of Share Amounts Used In Computing Earnings Per Share [Abstract]
Weighted average shares outstanding - basic (in shares)	144,087,000	143,765,000
Dilutive effect of assumed exercise of SAR's and vesting of performance shares (in shares)	1,242,000	1,173,000
Weighted average shares outstanding - diluted (in shares)	145,329,000	144,938,000
Antidilutive securities excluded from computation of earnings per share	58,000	88,000