Marketable Securities - Available-for-Sale (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost, current	$ 16,042	$ 25,736
Accumulated gross unrealized gains, current	1,486	2,699
Accumulated gross unrealized losses, current	(28)	(25)
Estimated fair value, current	17,500	28,410
Amortized cost, noncurrent	1,419	14,694
Accumulated gross unrealized gains, noncurrent	0	0
Accumulated gross unrealized losses, noncurrent	(22)	(47)
Estimated fair value, noncurrent	$ 1,397	14,647
Average remaining maturity, current	6 months
Average remaining maturity, noncurrent	21 months
Corporate notes and bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost, current	$ 15,517	23,056
Accumulated gross unrealized gains, current	0	0
Accumulated gross unrealized losses, current	(28)	(25)
Estimated fair value, current	15,489	23,031
Amortized cost, noncurrent	1,419	13,694
Accumulated gross unrealized gains, noncurrent	0	0
Accumulated gross unrealized losses, noncurrent	(22)	(45)
Estimated fair value, noncurrent	1,397	13,649
Agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost, noncurrent		1,000
Accumulated gross unrealized gains, noncurrent		0
Accumulated gross unrealized losses, noncurrent		(2)
Estimated fair value, noncurrent		998
Mortgage securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost, current	525	682
Accumulated gross unrealized gains, current	1,486	2,699
Accumulated gross unrealized losses, current	0	0
Estimated fair value, current	$ 2,011	3,381
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost, current		1,998
Accumulated gross unrealized gains, current		0
Accumulated gross unrealized losses, current		0
Estimated fair value, current		$ 1,998

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, Current, Average Remaining Maturity

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

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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=51813488&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=49167202&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
-Glossary Available-for-Sale Securities
-URI http://asc.fasb.org/extlink&oid=6505594

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=49167202&loc=d3e26626-111562

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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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