Investments Summary (Details) (USD $) In Thousands, unless otherwise specified	Mar. 29, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and available-for-sale investments, amortized cost	$ 246,639	$ 246,514
Cash equivalents and available-for-sale investments, gains	39	35
Cash equivalents and available-for-sale securities, losses	87	70
Total, fair value	246,591	246,479
Gross Amortized Cost and Estimated Fair Value of Investments
Due in one year or less, gross amortized cost	216,560	223,456
Due in one year or less, fair value	216,537	223,413
Due in one year through five years, gross amortized cost	30,079	23,059
Due after one year through five years, fair value	30,054	23,066
Total, amortized cost basis	246,639	246,515
Total, fair value	246,591	246,479
Commercial papers
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and available-for-sale investments, amortized cost	17,988	3,199
Total, fair value	17,988	3,199
Gross Amortized Cost and Estimated Fair Value of Investments
Total, fair value	17,988	3,199
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and available-for-sale investments, amortized cost	31,408	42,994
Total, fair value	31,408	42,994
Gross Amortized Cost and Estimated Fair Value of Investments
Total, fair value	31,408	42,994
U.S. treasury bills and notes
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and available-for-sale investments, amortized cost	6,028	6,067
Total, fair value	6,033	6,072
Gross Amortized Cost and Estimated Fair Value of Investments
Total, fair value	6,033	6,072
Securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and available-for-sale investments, amortized cost	191,215	194,254
Total, fair value	191,162	194,214
Gross Amortized Cost and Estimated Fair Value of Investments
Total, fair value	191,162	194,214
Accumulated other comprehensive income gains losses | Commercial papers
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and available-for-sale investments, gains	0	0
Cash equivalents and available-for-sale securities, losses	0	0
Accumulated other comprehensive income gains losses | Money market funds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and available-for-sale investments, gains	0	0
Cash equivalents and available-for-sale securities, losses	0	0
Accumulated other comprehensive income gains losses | U.S. treasury bills and notes
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and available-for-sale investments, gains	5	5
Cash equivalents and available-for-sale securities, losses	0	0
Accumulated other comprehensive income gains losses | Securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and available-for-sale investments, gains	34	30
Cash equivalents and available-for-sale securities, losses	87	70
Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Total, fair value	35,407	42,994
Gross Amortized Cost and Estimated Fair Value of Investments
Total, fair value	35,407	42,994
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Total, fair value	211,184	203,485
Gross Amortized Cost and Estimated Fair Value of Investments
Total, fair value	$ 211,184	$ 203,485