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, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator for earnings per share:
Earnings from continuing operations	$ 78,177	$ 55,949	$ 42,405	$ 48,825	$ 177,015	$ 225,356	$ 222,652
Loss from discontinued operations, net of tax	(916)	(44)	(1,312)	(686)	0	(2,958)	(1,178)
Net earnings for basic and diluted earnings per share					$ 177,015	$ 222,398	$ 221,474
Denominator for earnings per share:
Weighted average number of common shares outstanding					142,446	151,634	158,323
Assumed exercise of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method					2,149	1,960	2,528
Diluted shares outstanding					144,595	153,594	160,851