Fair Value (Details) (Recurring Basis [Member], USD $) In Thousands	Jul. 01, 2011	Dec. 31, 2010
Financial assets measured at fair value on a recurring basis
Total	$ 93,874	$ 92,233
Level 1 [Member]
Financial assets measured at fair value on a recurring basis
Total	27,616	68,395
Level 1 [Member] | Money market funds [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	27,616	68,395
Level 1 [Member] | Commercial Paper [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	0
Level 1 [Member] | Commercial Paper [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	0
Level 1 [Member] | Corporate bonds [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	0
Level 1 [Member] | Corporate bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	0	0
Level 1 [Member] | State, municipal and local government agencies bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	0	0
Level 1 [Member] | U.S. federal government bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	0
Level 2 [Member]
Financial assets measured at fair value on a recurring basis
Total	66,258	23,838
Level 2 [Member] | Money market funds [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	0	0
Level 2 [Member] | Commercial Paper [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	1,200
Level 2 [Member] | Commercial Paper [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	4,796
Level 2 [Member] | Corporate bonds [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	1,130
Level 2 [Member] | Corporate bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	22,849	11,907
Level 2 [Member] | State, municipal and local government agencies bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	32,261	11,931
Level 2 [Member] | U.S. federal government bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	4,022
Level 3 [Member]
Financial assets measured at fair value on a recurring basis
Total	0	0
Level 3 [Member] | Money market funds [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	0	0
Level 3 [Member] | Commercial Paper [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	0
Level 3 [Member] | Commercial Paper [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	0
Level 3 [Member] | Corporate bonds [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	0
Level 3 [Member] | Corporate bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	0	0
Level 3 [Member] | State, municipal and local government agencies bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	0	0
Level 3 [Member] | U.S. federal government bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	0
Money market funds [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	27,616	68,395
Commercial Paper [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	1,200
Commercial Paper [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	4,796
Corporate bonds [Member] | Cash and Cash Equivalents [Member]
Financial assets measured at fair value on a recurring basis
Total	1,130
Corporate bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	22,849	11,907
State, municipal and local government agencies bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	32,261	11,931
U.S. federal government bonds [Member] | Short-term Investments [Member]
Financial assets measured at fair value on a recurring basis
Total	$ 4,022