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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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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Fair Value of Financial Instruments - Fair Value Hierarchy for Financial Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Fair value hierarchy for its financial assets
Transfer of assets between Level 1 to Level 2	$ 0		$ 0
Transfer of assets between Level 2 to Level 1	0		$ 0
Fair Value, Measurements, Recurring
Fair value hierarchy for its financial assets
Total assets	4,213	$ 8,358
Fair Value, Measurements, Recurring \| Money market funds
Fair value hierarchy for its financial assets
Available-for-sale Securities		84
Fair Value, Measurements, Recurring \| U.S. government-sponsored enterprise bonds
Fair value hierarchy for its financial assets
Available-for-sale Securities		3,767
Fair Value, Measurements, Recurring \| Corporate notes
Fair value hierarchy for its financial assets
Available-for-sale Securities	3,913	480
Fair Value, Measurements, Recurring \| Municipal Bonds
Fair value hierarchy for its financial assets
Available-for-sale Securities	300	4,027
Fair Value, Measurements, Recurring \| Level 1
Fair value hierarchy for its financial assets
Total assets		84
Fair Value, Measurements, Recurring \| Level 1 \| Money market funds
Fair value hierarchy for its financial assets
Available-for-sale Securities		84
Fair Value, Measurements, Recurring \| Level 2
Fair value hierarchy for its financial assets
Total assets	4,213	8,274
Fair Value, Measurements, Recurring \| Level 2 \| U.S. government-sponsored enterprise bonds
Fair value hierarchy for its financial assets
Available-for-sale Securities		3,767
Fair Value, Measurements, Recurring \| Level 2 \| Corporate notes
Fair value hierarchy for its financial assets
Available-for-sale Securities	3,913	480
Fair Value, Measurements, Recurring \| Level 2 \| Municipal Bonds
Fair value hierarchy for its financial assets
Available-for-sale Securities	$ 300	$ 4,027