Fair Value (Details) (Recurring Basis [Member], USD $) In Thousands, unless otherwise specified	Mar. 30, 2012	Dec. 31, 2011
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	$ 125,289	$ 133,358
Total liabilities measured and recorded at fair value	660	159
Money market funds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	37,680	62,131
Certificates of deposit [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	1,325
State, municipal and local government agencies bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	47,825	38,825
Corporate bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	22,213	18,604
U.S. federal government bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	5,896	9,230
Commercial paper [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	10,181	4,195
Foreign exchange forward contracts[Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	169	373
Total liabilities measured and recorded at fair value	660	159
Level 1 [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	43,576	71,361
Total liabilities measured and recorded at fair value	0	0
Level 1 [Member] | Money market funds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	37,680	62,131
Level 1 [Member] | Certificates of deposit [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0
Level 1 [Member] | State, municipal and local government agencies bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 1 [Member] | Corporate bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 1 [Member] | U.S. federal government bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	5,896	9,230
Level 1 [Member] | Commercial paper [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 1 [Member] | Foreign exchange forward contracts[Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Total liabilities measured and recorded at fair value	0	0
Level 2 [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	81,713	61,997
Total liabilities measured and recorded at fair value	660	159
Level 2 [Member] | Money market funds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 2 [Member] | Certificates of deposit [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	1,325
Level 2 [Member] | State, municipal and local government agencies bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	47,825	38,825
Level 2 [Member] | Corporate bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	22,213	18,604
Level 2 [Member] | U.S. federal government bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 2 [Member] | Commercial paper [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	10,181	4,195
Level 2 [Member] | Foreign exchange forward contracts[Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	169	373
Total liabilities measured and recorded at fair value	660	159
Level 3 [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Total liabilities measured and recorded at fair value	0	0
Level 3 [Member] | Money market funds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 3 [Member] | Certificates of deposit [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0
Level 3 [Member] | State, municipal and local government agencies bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 3 [Member] | Corporate bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 3 [Member] | U.S. federal government bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 3 [Member] | Commercial paper [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Level 3 [Member] | Foreign exchange forward contracts[Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	0	0
Total liabilities measured and recorded at fair value	$ 0	$ 0