Fair Value (Details) (Recurring Basis [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	$ 133,358	$ 91,919
Total liabilities measured and recorded at fair value	159
Money market funds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	62,131	68,081
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	38,825	11,931
Corporate bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	18,604	11,907
U.S. federal government bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	9,230
Commercial Paper [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	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	373
Total liabilities measured and recorded at fair value	159
Level 1 [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	71,361	68,081
Total liabilities measured and recorded at fair value	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	62,131	68,081
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	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
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
Total liabilities measured and recorded at fair value	0
Level 2 [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	61,997	23,838
Total liabilities measured and recorded at fair value	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] | 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	38,825	11,931
Level 2 [Member] | Corporate bonds [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	18,604	11,907
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
Level 2 [Member] | Commercial Paper [Member]
Financial assets measured at fair value on a recurring basis
Total assets measured and recorded at fair value	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	373
Total liabilities measured and recorded at fair value	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
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] | 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
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
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
Total liabilities measured and recorded at fair value	$ 0