Summary of Significant Accounting Policies - Summary of Components of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost	$ 6,890	$ 18,843
Unrealized Losses	(24)	(78)
Market Value	6,866	18,765
U.S. Treasuries [Member]
Amortized Cost	2,578	1,744
Unrealized Losses	(3)
Market Value	2,575	1,744
Corporate Bonds [Member]
Amortized Cost	4,312	17,099
Unrealized Losses	(21)	(78)
Market Value	$ 4,291	$ 17,021

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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Amortized cost of 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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