Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Jan. 01, 2011
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	$ 94,964	$ 138,567
Total short-term investments	212,526	227,295
Total long-term investments	17,477	17,500
Assets and liabilities measured at fair value on recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	50,851	95,264
Total short-term investments	11,107	6,999
Total assets at fair value	61,958	102,263
Assets and liabilities measured at fair value on recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	50,851	45,167
Assets and liabilities measured at fair value on recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury bills
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents		50,097
Total short-term investments	8,600	6,999
Assets and liabilities measured at fair value on recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. government bonds
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	2,507
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents		2,659
Total short-term investments	201,419	220,296
Total assets at fair value	201,419	222,955
Derivative instruments	1,998	3,811
Total liabilities at fair value	1,998	3,811
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | Asset-backed securities
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	5,739
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | Corporate bonds
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	75,060	88,518
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | Variable-rate demand notes
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	41,280	39,425
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | U.S. government agency
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	19,836	34,680
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | Municipal bonds
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	56,984	38,414
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | International government bonds
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	950	10,830
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | Certificates of deposit
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	1,570	5,742
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | Commercial paper
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents		2,659
Total short-term investments		2,687
Assets and liabilities measured at fair value on recurring basis | Significant Unobservable Inputs (Level 3)
Financial assets and liabilities measured at fair value on a recurring basis
Total long-term investments	17,477	17,500
Total assets at fair value	17,477	17,500
Contingent consideration	876	1,780
Total liabilities at fair value	876	1,780
Assets and liabilities measured at fair value on recurring basis | Significant Unobservable Inputs (Level 3) | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Total long-term investments	17,477	17,500
Assets and liabilities measured at fair value on recurring basis | Fair Value
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	50,851	97,923
Total short-term investments	212,526	227,295
Total long-term investments	17,477	17,500
Total assets at fair value	280,854	342,718
Derivative instruments	1,998	3,811
Contingent consideration	876	1,780
Total liabilities at fair value	2,874	5,591
Assets and liabilities measured at fair value on recurring basis | Fair Value | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	50,851	45,167
Assets and liabilities measured at fair value on recurring basis | Fair Value | U.S. Treasury bills
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents		50,097
Total short-term investments	8,600	6,999
Assets and liabilities measured at fair value on recurring basis | Fair Value | Asset-backed securities
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	5,739
Assets and liabilities measured at fair value on recurring basis | Fair Value | U.S. government bonds
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	2,507
Assets and liabilities measured at fair value on recurring basis | Fair Value | Corporate bonds
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	75,060	88,518
Assets and liabilities measured at fair value on recurring basis | Fair Value | Variable-rate demand notes
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	41,280	39,425
Assets and liabilities measured at fair value on recurring basis | Fair Value | U.S. government agency
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	19,836	34,680
Assets and liabilities measured at fair value on recurring basis | Fair Value | Municipal bonds
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	56,984	38,414
Assets and liabilities measured at fair value on recurring basis | Fair Value | International government bonds
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	950	10,830
Assets and liabilities measured at fair value on recurring basis | Fair Value | Certificates of deposit
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	1,570	5,742
Assets and liabilities measured at fair value on recurring basis | Fair Value | Commercial paper
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents		2,659
Total short-term investments		2,687
Assets and liabilities measured at fair value on recurring basis | Fair Value | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Total long-term investments	$ 17,477	$ 17,500