Cash, cash equivalents, short-term investments and restricted cash - Summary of unrealized gains and losses (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 21,867	$ 42,843
Gross Unrealized Gains		4
Gross Unrealized Losses	(2)	(23)
Fair Value	21,865	42,824
Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	19,810	23,809
Fair Value	19,810	23,809
Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,057	19,034
Gross Unrealized Gains		4
Gross Unrealized Losses	(2)	(23)
Fair Value	2,055	19,015
Money market accounts
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	19,810	23,809
Fair Value	19,810	23,809
Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,307	199
Fair Value	1,307	199
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		9,438
Gross Unrealized Gains		4
Gross Unrealized Losses		(3)
Fair Value		9,439
Government-sponsored enterprise obligations
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		3,767
Gross Unrealized Losses		(10)
Fair Value		3,757
U.S. government securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	750	5,008
Gross Unrealized Losses	(2)	(10)
Fair Value	$ 748	4,998
Sovereign government bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		622
Fair Value		$ 622

This item represents the cost of debt 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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