Financial Instruments (Details 1) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Sep. 29, 2018	Sep. 29, 2018	Mar. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Equity Securities, Gross Unrealized Loss	$ 73	$ 6,300
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	336,075	336,075	$ 746,802
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(8,771)	(8,771)	(15,006)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	771,754	771,754	495,600
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(41,770)	(41,770)	(25,438)
Available-for-Sale Securities, Fair Value, Total	1,107,829	1,107,829	1,242,402
Available-for-Sale Securities, Gross Unrealized Losses, Total	(50,541)	(50,541)	(40,444)
Non-financial institution securities [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	44,067	44,067	69,780
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(748)	(748)	(1,146)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	19,640	19,640	8,344
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(546)	(546)	(230)
Available-for-Sale Securities, Fair Value, Total	63,707	63,707	78,124
Available-for-Sale Securities, Gross Unrealized Losses, Total	(1,294)	(1,294)	(1,376)
U.S. Government and Agency Securities [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	0	0	13,471
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	0	0	(176)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	15,507	15,507	9,176
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(337)	(337)	(96)
Available-for-Sale Securities, Fair Value, Total	15,507	15,507	22,647
Available-for-Sale Securities, Gross Unrealized Losses, Total	(337)	(337)	(272)
Mortgage-Backed Securities [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	222,604	222,604	510,988
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(5,996)	(5,996)	(11,048)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	497,433	497,433	299,663
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(20,860)	(20,860)	(11,263)
Available-for-Sale Securities, Fair Value, Total	720,037	720,037	810,651
Available-for-Sale Securities, Gross Unrealized Losses, Total	(26,856)	(26,856)	(22,311)
Asset-backed Securities [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	18,472	18,472	57,128
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(278)	(278)	(876)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	65,425	65,425	32,696
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(974)	(974)	(502)
Available-for-Sale Securities, Fair Value, Total	83,897	83,897	89,824
Available-for-Sale Securities, Gross Unrealized Losses, Total	(1,252)	(1,252)	(1,378)
Debt Mutual Fund [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	0	0	0
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	0	0	0
Available-for-Sale Securities, 12 Months or Greater, Fair Value	84,926	84,926	89,670
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(16,424)	(16,424)	(11,680)
Available-for-Sale Securities, Fair Value, Total	84,926	84,926	89,670
Available-for-Sale Securities, Gross Unrealized Losses, Total	(16,424)	(16,424)	(11,680)
Commercial Mortgage Backed Securities [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	44,231	44,231	95,435
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(950)	(950)	(1,760)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	88,823	88,823	56,051
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(2,629)	(2,629)	(1,667)
Available-for-Sale Securities, Fair Value, Total	133,054	133,054	151,486
Available-for-Sale Securities, Gross Unrealized Losses, Total	(3,579)	(3,579)	$ (3,427)
Equity Securities [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	6,701	6,701
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(799)	(799)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	0	0
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	0	0
Available-for-Sale Securities, Fair Value, Total	6,701	6,701
Available-for-Sale Securities, Gross Unrealized Losses, Total	$ (799)	$ (799)