Marketable Investment Securities, Restricted Cash and Cash Equivalents, and Other Investment Securities - Changes in Level 3 Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Fair values transfers between Level 1 and Level 2
Fair value assets transfer from level 1 to level 2	$ 0
Fair value liabilities transfer from level 1 to level 2		$ 0
Fair value assets transfer from level 2 to level 1	0
Fair value liabilities transfer from level 2 to level 1		0
Investment Securities \| Level 3
Level 3 Investment Securities
Balance at the beginning of the year	195	6,721
Net realized and unrealized gains (losses) included in earnings		(10,488)
Net realized and unrealized gains (losses) included in other comprehensive income (loss)	4	9,199
Sales		(5,099)
Settlements	(6)	(138)
Balance at the end of the year	$ 193	$ 195

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of transfers of liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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