Marketable Securities - Available-for-Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Marketable Securities, Current [Abstract]
Amortized cost basis, current	$ 401	$ 562
Accumulated gross unrealized gains, current	7,922	9,388
Accumulated gross unrealized losses, current	(2)	(7)
Fair value, current	8,321	9,943
Mortgage securities
Marketable Securities, Current [Abstract]
Amortized cost basis, current	398	450
Accumulated gross unrealized gains, current	7,922	9,341
Accumulated gross unrealized losses, current	0	0
Fair value, current	8,320	9,791
Equity securities
Marketable Securities, Current [Abstract]
Amortized cost basis, current	3	112
Accumulated gross unrealized gains, current	0	47
Accumulated gross unrealized losses, current	(2)	(7)
Fair value, current	$ 1	152
Corporate notes and bonds
Marketable Securities, Noncurrent [Abstract]
Amortized cost basis, non-current		26,607
Accumulated gross unrealized gains, non-current		0
Accumulated gross unrealized losses, non-current		(62)
Marketable securities, non-current:		$ 26,545

Available-for-sale Securities, Current, Accumulated Gross Unrealized Gains

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Available-for-sale Securities, Current, Accumulated Gross Unrealized Losses

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Available-for-sale Securities, Current, Amortized Cost Basis

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Available-for-sale Securities, Noncurrent, Accumulated Gross Unrealized Gains

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Available-for-sale Securities, Noncurrent, Accumulated Gross Unrealized Losses

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- Definition

Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ 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)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: 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=82896770&loc=d3e26626-111562

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Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

+ 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=82896770&loc=d3e26626-111562

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