Fair Value (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 30, 2012	Dec. 31, 2011
Summary of available-for-sale securities
Amortized Cost	$ 87,366	$ 70,819
Gross Unrealized Gains	81	56
Gross Unrealized Losses	(7)	(21)
Total short-term investments	87,440	70,854
Certificates of deposit [Member]
Summary of available-for-sale securities
Amortized Cost	1,324
Gross Unrealized Gains	1
Total short-term investments	1,325
State, municipal and local government agencies bonds [Member]
Summary of available-for-sale securities
Amortized Cost	47,758	38,785
Gross Unrealized Gains	67	46
Gross Unrealized Losses		(6)
Total short-term investments	47,825	38,825
Corporate bonds [Member]
Summary of available-for-sale securities
Amortized Cost	22,208	18,613
Gross Unrealized Gains	12	6
Gross Unrealized Losses	(7)	(15)
Total short-term investments	22,213	18,604
U.S. federal government bonds [Member]
Summary of available-for-sale securities
Amortized Cost	5,895	9,226
Gross Unrealized Gains	1	4
Total short-term investments	5,896	9,230
Commercial paper [Member]
Summary of available-for-sale securities
Amortized Cost	10,181	4,195
Total short-term investments	$ 10,181	$ 4,195