Investments and Fair Value of Financial Instruments - Summary of Amortized Cost and Fair Value of the Available-For-Sale Investment Securities Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 15,402	$ 52,613
Unrealized Gains	0	0
Unrealized Losses	(4)	(19)
Estimated Fair Value	15,398	52,594
Cash Equivalents [Member] \| Money Market Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,631	1,549
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	2,631	1,549
Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	3,900
Short-term Investments [Member] \| Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	980	3,049
Unrealized Gains	0	0
Unrealized Losses	0	(2)
Estimated Fair Value	980	3,047
Short-term Investments [Member] \| U.S. Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,001	19,267
Unrealized Gains	0	0
Unrealized Losses	(4)	(9)
Estimated Fair Value	4,997	19,258
Short-term Investments [Member] \| Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,290	21,248
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	4,290	21,248
Short-term Investments [Member] \| U.S. Government Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,500	5,000
Unrealized Gains	0	0
Unrealized Losses	0	(6)
Estimated Fair Value	$ 2,500	4,994
Long-term investments [Member] \| U.S. Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		2,500
Unrealized Gains		0
Unrealized Losses		(2)
Estimated Fair Value		$ 2,498

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
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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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
-Name Accounting Standards Codification
-Topic 320
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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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