Summary of Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Mar. 31, 2015
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	$ 471,485	$ 1,719,843
Available-for-sale, gross unrealized gains	447	15,011
Available-for-sale, gross unrealized losses	(99)	(474)
Available-for-sale, estimated fair value	471,833	1,734,380
Government agency bonds [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	468,290	741,780
Available-for-sale, gross unrealized gains	439	676
Available-for-sale, gross unrealized losses	(99)	(200)
Available-for-sale, estimated fair value	468,630	742,256
Municipal bonds [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost		41,552
Available-for-sale, gross unrealized gains		155
Available-for-sale, gross unrealized losses		(9)
Available-for-sale, estimated fair value		41,698
Auction rate securities [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost		9,825
Available-for-sale, gross unrealized gains		0
Available-for-sale, gross unrealized losses		0
Available-for-sale, estimated fair value		9,825
Time Deposits [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost		506
Available-for-sale, gross unrealized gains		0
Available-for-sale, gross unrealized losses		0
Available-for-sale, estimated fair value		506
Corporate bonds and debt [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	1,000	924,818
Available-for-sale, gross unrealized gains	0	2,376
Available-for-sale, gross unrealized losses	0	(265)
Available-for-sale, estimated fair value	1,000	926,929
Equity Securities [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	2,195	1,362
Available-for-sale, gross unrealized gains	8	11,804
Available-for-sale, gross unrealized losses	0	0
Available-for-sale, estimated fair value	$ 2,203	$ 13,166

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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