Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 27, 2014	Dec. 28, 2013
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	$ 111,705	$ 95,800
Total short-term investments	216,973	179,593
Total long-term investments	11,505	10,632
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	28,036	39,538
Total short-term investments	650
Total assets at fair value	28,686	39,538
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	28,036	39,538
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	650
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	20,385	10,718
Total short-term investments	216,323	179,593
Derivative instruments	507	513
Other assets, net	507	513
Total assets at fair value	237,215	190,824
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	14,147	2,499
Total short-term investments	11,439	3,748
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 cash equivalents	5,331	7,768
Total short-term investments	850
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 cash equivalents	907	451
Total short-term investments	143,449	119,460
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	36,014	17,844
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	15,755	38,025
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	5,687	516
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	2,528
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | US government agency
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	601
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	11,505	10,632
Total assets at fair value	11,505	10,632
Total liabilities at fair value	17,959	12,919
Assets and liabilities measured at fair value on recurring basis | Significant Unobservable Inputs (Level 3) | Accrued expenses:
Financial assets and liabilities measured at fair value on a recurring basis
Contingent consideration	6,279
Assets and liabilities measured at fair value on recurring basis | Significant Unobservable Inputs (Level 3) | Other non-current liabilities:
Financial assets and liabilities measured at fair value on a recurring basis
Contingent consideration	11,680	12,919
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	11,505	10,632
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	48,421	50,256
Total short-term investments	216,973	179,593
Total long-term investments	11,505	10,632
Derivative instruments	507	513
Other assets, net	507	513
Total assets at fair value	277,406	240,994
Total liabilities at fair value	17,959	12,919
Assets and liabilities measured at fair value on recurring basis | Fair Value | Accrued expenses:
Financial assets and liabilities measured at fair value on a recurring basis
Contingent consideration	6,279
Assets and liabilities measured at fair value on recurring basis | Fair Value | Other non-current liabilities:
Financial assets and liabilities measured at fair value on a recurring basis
Contingent consideration	11,680	12,919
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	28,036	39,538
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	14,147	2,499
Total short-term investments	11,439	3,748
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 cash equivalents	5,331	7,768
Total short-term investments	850
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 cash equivalents	907	451
Total short-term investments	143,449	119,460
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	36,014	17,844
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	15,755	38,025
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	5,687	516
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	2,528
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	650
Assets and liabilities measured at fair value on recurring basis | Fair Value | US government agency
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	601
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	$ 11,505	$ 10,632