Debt and Credit Agreements (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Long-term Debt	$ 960,706,000	$ 857,358,000
Less: current maturities	(3,278,000)	(3,558,000)
Total Long-term Debt	957,428,000	853,800,000
Cash payments for interest on all debt	45,500,000	46,400,000	59,900,000
Maturities of Long-term Debt [Abstract]
2014	14,770,000
2015	252,312,000
2016	1,357,000
2017	240,683,000
Senior notes | 5.75% notes due May 15, 2018
Debt Instrument [Line Items]
Stated interest rate	5.75%	5.75%
Long-term Debt	447,931,000	447,613,000
Redemption price as a percentage of principal amount of notes	101.00%
Senior notes | 5.125% notes due September 15, 2013
Debt Instrument [Line Items]
Stated interest rate	5.125%	5.125%
Long-term Debt	149,875,000	149,705,000
Senior notes | 2.7% notes due October 15, 2015
Debt Instrument [Line Items]
Stated interest rate	2.70%	2.70%
Long-term Debt	249,022,000	248,681,000
Redemption price as a percentage of principal amount of notes	101.00%
Other financing payable in varying amounts due principally through 2018 with a weighted-average interest rate of 2.7% and 9.4% at December 31, 2012 and 2011, respectively
Debt Instrument [Line Items]
Long-term Debt	$ 113,878,000	$ 11,359,000
Weighted average interest rate	2.70%	9.40%
Line of credit
Debt Instrument [Line Items]
Maximum debt to capital ratio per covenant	60.00%
Maximum proportion of subsidiary consolidated indebtedness to consolidated tangible assets	10.00%
Minimum consolidated interest coverage ratio, numerator	3
Minimum consolidated interest coverage ratio, denominator	1