Significant Accounting Policies, Cash, Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized cost	$ 49,415	$ 53,450
Gross unrealized gains	1	1
Gross unrealized losses	(24)	(42)
Fair value	49,392	53,409
Short-term Investments [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized cost	28,161	36,560
Gross unrealized gains	1	1
Gross unrealized losses	(24)	(42)
Fair value	28,138	36,519
Commercial Paper [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized cost	997	4,989
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	997	4,989
Corporate Notes and Bonds [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized cost	20,036	19,357
Gross unrealized gains	1	0
Gross unrealized losses	(19)	(40)
Fair value	20,018	19,317
U.S. Government Agency Securities [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized cost	5,917	10,941
Gross unrealized gains	0	1
Gross unrealized losses	(4)	(2)
Fair value	5,913	10,940
Cash and Cash Equivalents [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized cost	21,254	16,890
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	21,254	16,890
Cash [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized cost	7,654	7,593
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	7,654	7,593
Money Market Funds [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized cost	13,600	9,297
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	13,600	9,297
Certificates of Deposit [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Amortized cost	1,211	1,273
Gross unrealized gains	0	0
Gross unrealized losses	(1)	0
Fair value	$ 1,210	$ 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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-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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+ 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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