Earnings Per Share and Comprehensive Earnings (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings per Share
Net earnings	$ 105,166	$ 89,023	$ 52,669	$ 106,692
Less: earnings allocable to participating securities	1,012	1,713	544	2,133
Earnings available for shareholders	104,154	87,310	52,125	104,559
Basic earnings per share (in dollars per share)	$ 1.93	$ 1.65	$ 0.97	$ 2.01
Diluted earnings per share (in dollars per share)	$ 1.90	$ 1.64	$ 0.95	$ 2.00
Weighted average shares outstanding - basic (in shares)	54,004,000	52,965,000	53,936,000	52,027,000
Add: Dilutive effects of stock options and RSUs (in shares)	704,000	448,000	755,000	380,000
Weighted average shares outstanding - dilutive (in shares)	54,708,000	53,413,000	54,691,000	52,407,000
Options not included in the diluted earnings per share calculation (in shares)		800,000		1,200,000
Comprehensive earnings
Net earnings	105,166	89,023	52,669	106,692
Amortization of Accumulated other comprehensive loss related to de-designated hedges, net of income tax benefits of $5,836, $2,478, $11,673, and $4,563, respectively	9,522	4,044	19,045	7,444
Amortization of Accumulated other comprehensive loss related to de-designated hedges income tax benefit	5,837	2,478	11,673	4,563
Total comprehensive earnings	$ 114,688	$ 93,067	$ 71,714	$ 114,136