Cash, Cash Equivalents and Short-Term Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 01, 2012	Apr. 01, 2012
Investment assets, measured at fair value on a recurring basis
Investment assets	$ 191,110	$ 190,756
Percentage of total investment assets	100.00%	100.00%
Level 1 [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	23,973	19,370
Level 2 [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	167,137	171,386
Money market funds [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	6,222	3,088
Percentage of total investment assets	3.00%	2.00%
Money market funds [Member] | Level 1 [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	6,222	3,088
U.S. government and agency securities [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	47,270	44,826
Percentage of total investment assets	25.00%	23.00%
U.S. government and agency securities [Member] | Level 1 [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	17,751	16,282
Corporate bonds and notes [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	67,009	69,234
Percentage of total investment assets	35.00%	36.00%
Corporate bonds and notes [Member] | Level 2 [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	67,009	69,234
Asset-backed securities [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	27,433	26,364
Percentage of total investment assets	14.00%	14.00%
Asset-backed securities [Member] | Level 2 [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	27,433	26,364
Mortgage-backed securities [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	43,176	47,244
Percentage of total investment assets	23.00%	25.00%
Mortgage-backed securities [Member] | Level 2 [Member]
Investment assets, measured at fair value on a recurring basis
Investment assets	$ 43,176	$ 47,244