Available-for-Sale Securities (Details) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)
Available-for-sale securities
Amortized Cost	$ 14,935
Gross unrealized losses	(4)
Fair Value	$ 14,931	$ 0
Number of available-for-sale securities in an unrealized loss position \| item	15
Number of available-for-sale securities in an unrealized loss position more than 12 months \| item	0
Unrealized loss position, available-for-sale securities	$ 13,000
Proceeds from sales of available for sale securities	7,800	$ 0
Corporate debt securities
Available-for-sale securities
Amortized Cost	13,934
Gross unrealized losses	(4)
Fair Value	13,930
U.S. government-sponsored securities
Available-for-sale securities
Amortized Cost	1,001
Fair Value	$ 1,001

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

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=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

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Number of investment positions in available-for-sale investments that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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No definition available.

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The cash inflow associated with the sale of debt securities classified as available-for-sale securities.

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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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