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Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair value of assets measured at fair value on a recurring basis
Marketable securities	$ 32,502	$ 44,066
Marketable securities
Available for sale securities in an unrealized loss position	32,500
Available for sale securities, unrealized loss	17
Recurring
Fair value of assets measured at fair value on a recurring basis
Marketable securities		44,066
Total fair value financial instruments	47,721	62,930
Recurring | U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Marketable securities	32,502	42,512
Recurring | Corporate debt securities
Fair value of assets measured at fair value on a recurring basis
Marketable securities		1,554
Recurring | Cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	4,061	2,785
Recurring | Money market funds
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	11,158	9,647
Recurring | U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		4,000
Recurring | Total cash and cash equivalents
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	15,219	16,432
Recurring | Restricted cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		2,432
Recurring | Quoted prices in active markets (Level 1)
Fair value of assets measured at fair value on a recurring basis
Marketable securities		0
Total fair value financial instruments	15,219	14,864
Recurring | Quoted prices in active markets (Level 1) | U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Marketable securities	0	0
Recurring | Quoted prices in active markets (Level 1) | Corporate debt securities
Fair value of assets measured at fair value on a recurring basis
Marketable securities		0
Recurring | Quoted prices in active markets (Level 1) | Cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	4,061	2,785
Recurring | Quoted prices in active markets (Level 1) | Money market funds
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	11,158	9,647
Recurring | Quoted prices in active markets (Level 1) | U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		0
Recurring | Quoted prices in active markets (Level 1) | Total cash and cash equivalents
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	15,219	12,432
Recurring | Quoted prices in active markets (Level 1) | Restricted cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		2,432
Recurring | Significant other observable inputs (Level 2)
Fair value of assets measured at fair value on a recurring basis
Marketable securities		44,066
Total fair value financial instruments	32,502	48,066
Recurring | Significant other observable inputs (Level 2) | U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Marketable securities	32,502	42,512
Recurring | Significant other observable inputs (Level 2) | Corporate debt securities
Fair value of assets measured at fair value on a recurring basis
Marketable securities		1,554
Recurring | Significant other observable inputs (Level 2) | Cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Recurring | Significant other observable inputs (Level 2) | Money market funds
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Recurring | Significant other observable inputs (Level 2) | U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		4,000
Recurring | Significant other observable inputs (Level 2) | Total cash and cash equivalents
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	4,000
Recurring | Significant other observable inputs (Level 2) | Restricted cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		0
Recurring | Significant unobservable inputs (Level 3)
Fair value of assets measured at fair value on a recurring basis
Marketable securities		0
Total fair value financial instruments	0	0
Recurring | Significant unobservable inputs (Level 3) | U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Marketable securities	0	0
Recurring | Significant unobservable inputs (Level 3) | Corporate debt securities
Fair value of assets measured at fair value on a recurring basis
Marketable securities		0
Recurring | Significant unobservable inputs (Level 3) | Cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Recurring | Significant unobservable inputs (Level 3) | Money market funds
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Recurring | Significant unobservable inputs (Level 3) | U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents
Recurring | Significant unobservable inputs (Level 3) | Total cash and cash equivalents
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	$ 0	0
Recurring | Significant unobservable inputs (Level 3) | Restricted cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		$ 0

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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