Nature of Business and Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011		Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator for earnings per share:
Earnings from continuing operations	$ 78,177	$ 55,949	$ 42,405	$ 48,825	$ 76,835	$ 64,390	$ 29,822	[1]	$ 51,605	$ 225,356	$ 222,652	$ 248,374
Loss from discontinued operations, net of tax	(916)	(44)	(1,312)	(686)	(705)	329	(513)		(289)	(2,958)	(1,178)	(248)
Net earnings for basic earnings per share										222,398	221,474	248,126
Interest associated with convertible notes, net of tax										0	0	935
Net earnings available to common shareholders - diluted										$ 222,398	$ 221,474	$ 249,061
Denominator for earnings per share:
Weighted average number of common shares outstanding										151,634	158,323	156,141
Assumed exercise of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method										1,960	2,528	3,196
Assumed conversion of convertible notes										0	0	2,293
Diluted shares outstanding										153,594	160,851	161,630

[1] Earnings from continuing operations for the second quarter of 2011 include the payment of a $39.0 million litigation settlement. See Note 13 to the Consolidated Financial Statements for additional information.