Long-term Debt (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Line of Credit Facility [Line Items]
Long-term debt, revolving credit facility	$ 649,500	$ 585,000
Compliance with covenants	The Company was in compliance with all covenants
Senior Credit Facility [Member]
Line of Credit Facility [Line Items]
Principal borrowing capacity, maximum	770,000
Remaining borrowing capacity	119,475
Line of credit facility, initiation date	Oct. 18, 2005
Line of credit facility, expiration date	Jun. 28, 2016
Interest rate description	The base rate of U.S. dollar-denominated loans is defined as the higher of the Bank of America prime rate or the Federal Funds rate plus .50%.
Credit facility commitment fee, minimum (in hundredths)	0.375%
Credit facility commitment fee, maximum (in hundredths)	0.50%
Interest rate swap period	4 years
Option to increase domestic		250,000
Domestic Line Of Credit [Member]
Line of Credit Facility [Line Items]
Principal borrowing capacity, maximum	745,000
Remaining borrowing capacity	649,500
Index rate or LIBOR plus (in hundredths)	2.22%	2.05%
Revolving credit facility period	5 years
Interest rate description	interest at Base Rate or LIBOR plus applicable margin	interest at Base Rate or LIBOR plus applicable margin
Foreign Line of Credit [Member]
Line of Credit Facility [Line Items]
Principal borrowing capacity, maximum	25,000	25,000
Revolving credit facility period		5 years
Interest rate description	interest at Base Rate or LIBOR plus applicable margin	interest at Base Rate or LIBOR plus applicable margin
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letter of credit amount outstanding	$ 1,025