Debt (Textuals) (Details)	12 Months Ended						3 Months Ended			3 Months Ended				12 Months Ended				12 Months Ended		12 Months Ended			12 Months Ended			12 Months Ended			12 Months Ended	3 Months Ended			12 Months Ended
	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2012 Senior A Notes Due 2022 [Member]	Dec. 31, 2012 Senior B Notes Due 2024 [Member]	Dec. 31, 2012 Senior C Notes Due 2027 [Member]	Jun. 30, 2012 Revolving Credit Facility Due 2014 [Member] USD ($)	Dec. 31, 2012 Revolving Credit Facility Due 2014 [Member] USD ($)	Dec. 31, 2011 Revolving Credit Facility Due 2014 [Member] USD ($)	Jun. 30, 2012 Revolving Credit Facility Due 2017 [Member] USD ($)	Dec. 31, 2012 Revolving Credit Facility Due 2017 [Member] USD ($)	Dec. 31, 2012 Revolving Credit Facility Due 2017 [Member] JPY (¥)	Dec. 31, 2011 Revolving Credit Facility Due 2017 [Member] USD ($)	Dec. 31, 2012 $50 Million Credit Facility [Member] USD ($)	Dec. 31, 2012 Term Loan Due 2018 [Member] USD ($)	Dec. 31, 2011 Term Loan Due 2018 [Member] USD ($)	Dec. 31, 2012 Senior Floating Notes [Member] USD ($) instrument	Dec. 31, 2011 Series A Floating Rate Notes Due 2012 [Member] USD ($)	Dec. 31, 2012 Series A Floating Rate Notes Due 2012 [Member] USD ($)	Dec. 31, 2012 Series B Floating Rate Notes Due 2015 [Member] USD ($)	Dec. 31, 2011 Series B Floating Rate Notes Due 2015 [Member] USD ($)	Dec. 31, 2012 Euro-denominated Notes [Member] EUR (€)	Dec. 31, 2012 EURO Note A Due 2013 [Member] USD ($)	Dec. 31, 2012 EURO Note A Due 2013 [Member] EUR (€)	Dec. 31, 2011 EURO Note A Due 2013 [Member] USD ($)	Dec. 31, 2012 EURO Note B Due 2016 [Member] USD ($)	Dec. 31, 2012 EURO Note B Due 2016 [Member] EUR (€)	Dec. 31, 2011 EURO Note B Due 2016 [Member] USD ($)	Dec. 31, 2012 Convertible Debt Due 2047 [Member] USD ($)	Jun. 30, 2012 Convertible Debt Due 2047 [Member] USD ($)	Dec. 31, 2012 Convertible Debt Due 2047 [Member] USD ($)	Dec. 31, 2011 Convertible Debt Due 2047 [Member] USD ($)	Dec. 31, 2012 Senior Notes [Member] USD ($)	Dec. 31, 2012 Senior Notes [Member] Senior A Notes Due 2022 [Member] USD ($)	Dec. 31, 2011 Senior Notes [Member] Senior A Notes Due 2022 [Member] USD ($)	Dec. 31, 2012 Senior Notes [Member] Senior B Notes Due 2024 [Member] USD ($)	Dec. 31, 2011 Senior Notes [Member] Senior B Notes Due 2024 [Member] USD ($)	Dec. 31, 2012 Senior Notes [Member] Senior C Notes Due 2027 [Member] USD ($)	Dec. 31, 2011 Senior Notes [Member] Senior C Notes Due 2027 [Member] USD ($)	Dec. 31, 2012 Letter of Credit [Member] Revolving Credit Facility Due 2017 [Member] USD ($)	Feb. 26, 2013 Subsequent Event [Member] $50 Million Credit Facility [Member] USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, expiration date										Apr. 30, 2017
Line of Credit Facility, current borrowing capacity										$ 300,000,000
Line of Credit Facility, maximum borrowing capacity										350,000,000				50,000,000
Credit facility is available for swing-line loans										30,000,000
Credit available for the issuance of letters of credit										30,000,000
Line of credit interest rate margin added to Libor at minimum (in hundredths)										1.25%
Line of credit interest rate margin added to Libor at maximum (in hundredths)										2.25%
Debt issuance cost							800,000			1,600,000																							1,200,000
Long-term debt	411,500,000	349,400,000							6,400,000		71,500,000	5,800,000			35,300,000		75,000,000				25,000,000		26,900,000		26,300,000	80,800,000		79,000,000			3,100,000	161,500,000	168,000,000	42,000,000		53,000,000		73,000,000
Line of Credit, current											5,700,000
Line of Credit, noncurrent											65,800,000
Outstanding amount																																								3,600,000	42,800,000
Line of Credit Facility, unused commitment level											224,900,000
Term of debt														5 years									7 years	7 years		10 years	10 years
Variable rate basis														one-month LIBOR						LIBOR
Basis spread on variable interest rate														1.50%						0.90%
Credit facility agreement, leverage ratio description														total leverage ratio no greater than 3.50 to 1.00
Credit facility agreement, interest coverage ratio description														interest coverage ratio greater than or equal to 2.50 to 1.00
Debt issuance costs														300,000
Number of tranches																	2
Debt Instrument, face amount																		50,000,000		25,000,000		81,500,000		20,400,000			61,100,000
Debt instrument, maturity date																		Jul. 28, 2012		Jul. 28, 2015			Feb. 27, 2013	Feb. 27, 2013		Feb. 27, 2016	Feb. 27, 2016		Mar. 15, 2047
Debt instrument, stated interest rate				3.67%	3.82%	4.02%					1.71%	1.71%			5.41%					1.21%			4.215%	4.215%		4.38%	4.38%		4.00%		4.00%			3.67%		3.82%		4.02%
Long-term debt	378,800,000	299,300,000																											161,500,000
Conversion ratio of debt per $1,000 of debt																													18.1227
Convertbile debt, conversion price (in usd per share)																													$ 55.18
Debentures automatic conversion feature																													Subsequent to March 20, 2012, if our common stock closing price exceeds 150% of the then prevailing conversion price for at least 20 trading days during any 30 consecutive trading day period, we have the option to cause the debentures to be automatically converted into West shares at the prevailing conversion rate
Debt instrument, repurchase amount																														158,400,000
Percentage of convertible debt repurchased																														98.06%
Purchase price paid for convertible debt																														1,038.91
Loss on debt extinguishment																														11,600,000
Purchase premium paid, convertible debt																														6,200,000
Write off of unamortized debt issuance costs																														4,400,000
Payments of debt extinguishment costs																														1,000,000
Weighted average of the coupon interest rate																																	3.87%
Annual effective interest rate																																	4.16%
Interest expense	18,600,000	19,300,000	17,700,000
Aggregate annual maturities of long-term debt [Abstract]
2014	100,000
2015	25,000,000
2016	81,500,000
2017	65,800,000
2018	35,300,000
Thereafter	$ 171,100,000