Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Summary of financial assets measured at fair value on recurring basis
Short-term investments	$ 223,592
Level 1 [Member]
Summary of financial assets measured at fair value on recurring basis
Short-term investments	223,592
Level 1 [Member] | Interest Rate Swap [Member]
Summary of financial assets measured at fair value on recurring basis
Intangible and other long-term assets	0	0
Level 1 [Member] | Non-qualified deferred compensation assets [Member]
Summary of financial assets measured at fair value on recurring basis
Intangible and other long-term assets	810	812
Level 1 [Member] | Non-qualified deferred compensation liabilities [Member]
Summary of financial assets measured at fair value on recurring basis
Accounts payable	0	1,429
Other long-term liabilities	0	0
Level 2 [Member]
Summary of financial assets measured at fair value on recurring basis
Short-term investments	0
Level 2 [Member] | Interest Rate Swap [Member]
Summary of financial assets measured at fair value on recurring basis
Intangible and other long-term assets	1,340	161
Level 2 [Member] | Non-qualified deferred compensation assets [Member]
Summary of financial assets measured at fair value on recurring basis
Intangible and other long-term assets	9,414	10,008
Level 2 [Member] | Non-qualified deferred compensation liabilities [Member]
Summary of financial assets measured at fair value on recurring basis
Accounts payable	2,655	1,524
Other long-term liabilities	12,407	14,236
Level 3 [Member]
Summary of financial assets measured at fair value on recurring basis
Short-term investments	0
Level 3 [Member] | Interest Rate Swap [Member]
Summary of financial assets measured at fair value on recurring basis
Intangible and other long-term assets	0	0
Level 3 [Member] | Non-qualified deferred compensation assets [Member]
Summary of financial assets measured at fair value on recurring basis
Intangible and other long-term assets	0	0
Level 3 [Member] | Non-qualified deferred compensation liabilities [Member]
Summary of financial assets measured at fair value on recurring basis
Accounts payable	0	0
Other long-term liabilities	0	0
Interest Rate Swap [Member]
Summary of financial assets measured at fair value on recurring basis
Intangible and other long-term assets	1,340	161
Non-qualified deferred compensation assets [Member]
Summary of financial assets measured at fair value on recurring basis
Intangible and other long-term assets	10,224	10,820
Non-qualified deferred compensation liabilities [Member]
Summary of financial assets measured at fair value on recurring basis
Accounts payable	2,655	2,953
Other long-term liabilities	$ 12,407	$ 14,236