Selected Quarterly Financial Data - (Unaudited) (Details) (USD $)	3 Months Ended					12 Months Ended			3 Months Ended								12 Months Ended			3 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2012 Quarter 1 [Member]	Mar. 31, 2011 Quarter 1 [Member]	Jun. 30, 2012 Quarter 2 [Member]	Jun. 30, 2011 Quarter 2 [Member]	Sep. 30, 2012 Quarter 3 [Member]	Sep. 30, 2011 Quarter 3 [Member]	Dec. 31, 2012 Quarter 4 [Member]	Dec. 31, 2011 Quarter 4 [Member]	Dec. 31, 2012 Supplemental Employee Retirement Plans, Defined Benefit [Member]	Dec. 31, 2011 Supplemental Employee Retirement Plans, Defined Benefit [Member]	Dec. 31, 2010 Supplemental Employee Retirement Plans, Defined Benefit [Member]	Dec. 31, 2012 Supplemental Employee Retirement Plans, Defined Benefit [Member] Corporate [Member]
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments																	$ (2,162,000)	$ 0	$ 0	$ (1,800,000)
Current Foreign Tax Expense (Benefit)	(4,500,000)					2,345,000	1,712,000	1,892,000
Current Foreign Tax Expense (Benefit) For Open Tax Years			400,000
Revenues						691,509,000	638,793,000	596,076,000	129,169,000	115,281,000	173,621,000	165,301,000	210,413,000	192,321,000	178,306,000	165,890,000
Operating income						193,142,000	171,863,000	160,762,000	31,065,000	25,679,000	51,590,000	45,122,000	65,253,000	62,400,000	45,234,000	38,662,000
Income before income taxes						169,168,000	158,057,000	158,211,000	30,233,000	21,923,000	47,939,000	42,114,000	55,668,000	56,966,000	35,328,000	37,054,000
Net income						120,687,000	110,396,000	107,441,000	19,997,000	15,730,000	31,862,000	27,578,000	44,377,000	42,302,000	24,451,000	24,786,000
Per basic share [Abstract]
Net income						$ 2.08	$ 1.86	$ 1.80	$ 0.34	$ 0.26	$ 0.55	$ 0.46	$ 0.77	$ 0.71	$ 0.42	$ 0.42
Per diluted share [Abstract]
Net income						$ 2.07	$ 1.85	$ 1.80	$ 0.34	$ 0.26	$ 0.55	$ 0.46	$ 0.76	$ 0.71	$ 0.42	$ 0.42
Termination Benefits Included In Operating results		3,600,000	400,000	300,000	100,000
Impairment of Long-Lived Assets to be Disposed of					1,800,000
Tax Adjustments, Settlements, and Unusual Provisions					1,400,000
Additional current federal tax expense (benefit)			1,700,000
Increases for tax positions related to the current year			$ 1,900,000			$ 0	$ 2,062,000	$ 2,563,000