Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair value
Investments available-for-sale		$ 1,776
U.S. government security funds
Fair value
Investments available-for-sale		1,776
Recurring basis \| Total
Fair value
Trading investment securities	$ 1,786	1,391
Total assets measured at fair value on a recurring basis	1,786	3,167
Recurring basis \| Total \| U.S. government security funds
Fair value
Investments available-for-sale		1,776
Recurring basis \| Level 1 - Quoted Prices in Active Markets for Identical Assets
Fair value
Trading investment securities	1,786	1,391
Total assets measured at fair value on a recurring basis	1,786	3,167
Recurring basis \| Level 1 - Quoted Prices in Active Markets for Identical Assets \| U.S. government security funds
Fair value
Investments available-for-sale		1,776
Recurring basis \| Level 2 - Significant Other Observable Inputs
Fair value
Trading investment securities	0	0
Total assets measured at fair value on a recurring basis	0	0
Recurring basis \| Level 2 - Significant Other Observable Inputs \| U.S. government security funds
Fair value
Investments available-for-sale		0
Recurring basis \| Level 3 - Significant Unobservable Inputs
Fair value
Trading investment securities	0	0
Total assets measured at fair value on a recurring basis	$ 0	0
Recurring basis \| Level 3 - Significant Unobservable Inputs \| U.S. government security funds
Fair value
Investments available-for-sale		$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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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)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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+ References

No definition available.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26626-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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