Cash, Cash Equivalents and Short-Term Marketable Securities - Unrealized Losses and Fair Values of Our Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Apr. 01, 2012
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	$ 23,229	$ 47,811
Gross Unrealized Losses, Less than 12 months	(120)	(196)
Fair Value, 12 months or greater	6,444	6,203
Gross Unrealized Losses, 12 months or greater	(89)	(90)
Fair Value, Total	29,673	54,014
Gross Unrealized Losses, Total	(209)	(286)
U.S. government and agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	1,999	15,585
Gross Unrealized Losses, Less than 12 months	(1)	(30)
Fair Value, Total	1,999	15,585
Gross Unrealized Losses, Total	(1)	(30)
State and Local Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	520	590
Gross Unrealized Losses, Less than 12 months		(20)
Fair Value, 12 months or greater	497
Gross Unrealized Losses, 12 months or greater	(3)
Fair Value, Total	1,017	590
Gross Unrealized Losses, Total	(3)	(20)
Corporate bonds and notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	6,271	11,685
Gross Unrealized Losses, Less than 12 months	(7)	(33)
Fair Value, 12 months or greater	496
Gross Unrealized Losses, 12 months or greater	(4)
Fair Value, Total	6,767	11,685
Gross Unrealized Losses, Total	(11)	(33)
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	922	3,516
Gross Unrealized Losses, Less than 12 months	(9)	(5)
Fair Value, 12 months or greater	1,879	3,786
Gross Unrealized Losses, 12 months or greater	(14)	(39)
Fair Value, Total	2,801	7,302
Gross Unrealized Losses, Total	(23)	(44)
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	13,517	16,435
Gross Unrealized Losses, Less than 12 months	(103)	(108)
Fair Value, 12 months or greater	3,572	2,417
Gross Unrealized Losses, 12 months or greater	(68)	(51)
Fair Value, Total	17,089	18,852
Gross Unrealized Losses, Total	$ (171)	$ (159)