Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Mar. 28, 2015	Dec. 27, 2014
Assets
Total Assets	$ 324,548	$ 325,705
Money market funds
Assets
Total Assets	39,633	21,478
Certificates of deposit
Assets
Total Assets	9,465	8,060
Commercial paper
Assets
Total Assets	21,690	46,072
Corporate bonds
Assets
Total Assets	223,238	235,285
U.S. agency notes
Assets
Total Assets	14,508	0
U.S. treasuries
Assets
Total Assets	16,014	14,810
Foreign currency exchange forward contracts
Assets
Total Assets	0	0
Liabilities
Total Liabilities	(117)	(64)
Level 1
Assets
Total Assets	55,647	36,288
Level 1 | Money market funds
Assets
Total Assets	39,633	21,478
Level 1 | Certificates of deposit
Assets
Total Assets	0	0
Level 1 | Commercial paper
Assets
Total Assets	0	0
Level 1 | Corporate bonds
Assets
Total Assets	0	0
Level 1 | U.S. agency notes
Assets
Total Assets	0	0
Level 1 | U.S. treasuries
Assets
Total Assets	16,014	14,810
Level 1 | Foreign currency exchange forward contracts
Assets
Total Assets	0	0
Liabilities
Total Liabilities	0	0
Level 2
Assets
Total Assets	268,901	289,417
Level 2 | Money market funds
Assets
Total Assets	0	0
Level 2 | Certificates of deposit
Assets
Total Assets	9,465	8,060
Level 2 | Commercial paper
Assets
Total Assets	21,690	46,072
Level 2 | Corporate bonds
Assets
Total Assets	223,238	235,285
Level 2 | U.S. agency notes
Assets
Total Assets	14,508	0
Level 2 | U.S. treasuries
Assets
Total Assets	0	0
Level 2 | Foreign currency exchange forward contracts
Assets
Total Assets	0	0
Liabilities
Total Liabilities	(117)	(64)
Level 3
Assets
Total Assets	0	0
Level 3 | Money market funds
Assets
Total Assets	0	0
Level 3 | Certificates of deposit
Assets
Total Assets	0	0
Level 3 | Commercial paper
Assets
Total Assets	0	0
Level 3 | Corporate bonds
Assets
Total Assets	0	0
Level 3 | U.S. agency notes
Assets
Total Assets	0	0
Level 3 | U.S. treasuries
Assets
Total Assets	0	0
Level 3 | Foreign currency exchange forward contracts
Assets
Total Assets	0	0
Liabilities
Total Liabilities	$ 0	$ 0