Summary of Significant Accounting Policies - Summary of Components of Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Amortized Cost	$ 6,829	$ 18,687
Unrealized Gains
Unrealized Losses	(53)	(78)
Market Value	6,776	18,765
U.S. Treasuries [Member]
Amortized Cost	929	1,744
Unrealized Gains
Unrealized Losses
Market Value	929	1,744
Corporate Bonds [Member]
Amortized Cost	5,900	16,943
Unrealized Gains
Unrealized Losses	(53)	(78)
Market Value	$ 5,847	$ 17,021

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in marketable security, classified as current.

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