Marketable Investment Securities, Restricted Cash and Cash Equivalents, and Other Investment Securities - Changes in Estimated Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair value of marketable investment securities in a loss position
Total	$ 135,598	$ 444,485
Unrealized loss on marketable investment securities in a loss position
Total	(151)	(276)
Debt securities
Fair value of marketable investment securities in a loss position
Less than 12 Months	111,505	410,145
12 Months or More	24,093	34,340
Unrealized loss on marketable investment securities in a loss position
Less than 12 Months	(68)	(156)
12 Months or More	$ (83)	$ (120)

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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