v3.8.0.1

Investments, AFS Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	$ 1,016,733	$ 500,973
Available-for-sale, gross unrealized gain	2,351	978
Available-for-sale, gross unrealized loss	(1,638)	(406)
Estimated Fair Value	1,017,446	501,545
Marketable equity securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	707	707
Available-for-sale, gross unrealized gain	2,236	879
Available-for-sale, gross unrealized loss	0	0
Estimated Fair Value	2,943	$ 1,586
Due in one year or less
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	397,536
Available-for-sale, gross unrealized gain	2
Available-for-sale, gross unrealized loss	(177)
Estimated Fair Value	397,361
Due after one year and through five years
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	618,490
Available-for-sale, gross unrealized gain	113
Available-for-sale, gross unrealized loss	(1,461)
Estimated Fair Value	617,142
Due after five years and through ten years
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	0
Available-for-sale, gross unrealized gain	0
Available-for-sale, gross unrealized loss	0
Estimated Fair Value	0
Due after ten years
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	0
Available-for-sale, gross unrealized gain	0
Available-for-sale, gross unrealized loss	0
Estimated Fair Value	0
Total
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	1,016,026
Available-for-sale, gross unrealized gain	115
Available-for-sale, gross unrealized loss	(1,638)
Estimated Fair Value	$ 1,014,503

X

- Definition

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
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+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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