Organization and Summary of Significant Accounting Policies, Cash, Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	$ 49,317	$ 53,450
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(84)	(42)
Fair Value	49,233	53,409
Short-Term Investments [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	31,266	36,560
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(83)	(42)
Fair Value	31,183	36,519
Commercial Paper [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	2,494	4,989
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	2,493	4,989
Corporate Notes and Bonds [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	22,846	19,357
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(76)	(40)
Fair Value	22,770	19,317
U.S. Government Agency Securities [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	4,719	10,941
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(4)	(2)
Fair Value	4,715	10,940
Cash and Cash Equivalents [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	18,051	16,890
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	18,050	16,890
Cash [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	7,408	7,593
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	7,408	7,593
Money Market Fund [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	10,643	9,297
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	10,642	9,297
Certificates of Deposit [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized Cost	1,207	1,273
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	0
Fair Value	$ 1,205	$ 1,273

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=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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Amount before tax of unrealized gain 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
-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 2
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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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-Paragraph 2
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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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