Investments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Sep. 28, 2014	Mar. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	$ 384,493	$ 362,604
U.S. government treasuries and agencies securities
Schedule of Available-for-sale Securities [Line Items]
Cost	119,455	112,268
Gross Unrealized Gains	112	76
Gross Unrealized Losses	(69)	(91)
Estimated Fair Value	119,498	112,253
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Cost	56,254	53,430
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	56,254	53,430
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost	23,179	22,330
Gross Unrealized Gains	10	11
Gross Unrealized Losses	(10)	(9)
Estimated Fair Value	23,179	22,332
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Cost	211,631	199,598
Gross Unrealized Gains	292	335
Gross Unrealized Losses	(166)	(127)
Estimated Fair Value	211,757	199,806
International government bonds
Schedule of Available-for-sale Securities [Line Items]
Cost	1,012	3,023
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(9)	(9)
Estimated Fair Value	1,003	3,014
Corporate commercial paper
Schedule of Available-for-sale Securities [Line Items]
Cost	9,695	6,246
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	9,695	6,246
Bank deposits
Schedule of Available-for-sale Securities [Line Items]
Cost	20,417	18,538
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	20,417	18,538
Repurchase agreements
Schedule of Available-for-sale Securities [Line Items]
Cost	1,132	46
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	1,132	46
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Cost	8,036	9,196
Gross Unrealized Gains	35	32
Gross Unrealized Losses	(11)	(18)
Estimated Fair Value	8,060	9,210
Total available-for-sale investments
Schedule of Available-for-sale Securities [Line Items]
Cost	450,811	424,675
Gross Unrealized Gains	449	454
Gross Unrealized Losses	(265)	(254)
Estimated Fair Value	450,995	424,875
Less amounts classified as cash equivalents
Schedule of Available-for-sale Securities [Line Items]
Cost	66,502	62,271
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	66,502	62,271
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Cost	384,309	362,404
Gross Unrealized Gains	449	454
Gross Unrealized Losses	(265)	(254)
Estimated Fair Value	$ 384,493	$ 362,604