Cash Equivalents and Available for Sale Marketable Securities - Schedule of Cash Equivalents and Available-for-sale Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019		Dec. 31, 2018
Money market funds	$ 37		$ 7
Commercial paper	19,984		20,678
U.S. government debt securities	8,105		3,226
Total cash equivalents	28,126	[1]	23,911	[2]
Commercial paper			714
Corporate debt securities	12,342		5,448
Total short-term investments	12,342		6,162
Total	40,468		30,073
Amortized Cost [Member]
Money market funds	37		7
Commercial paper	19,960		20,648
U.S. government debt securities	8,074		3,224
Total cash equivalents	28,071	[1]	23,879	[2]
Commercial paper			714
Corporate debt securities	12,318		5,444
Total short-term investments	12,318		6,158
Total	40,389		30,037
Unrealized Gains [Member]
Money market funds
Commercial paper	24		30
U.S. government debt securities	31		2
Total cash equivalents	55	[1]	32	[2]
Commercial paper
Corporate debt securities	24		5
Total short-term investments	24		5
Total	79		37
Unrealized Losses [Member]
Money market funds
Commercial paper
U.S. government debt securities
Total cash equivalents		[1]		[2]
Commercial paper
Corporate debt securities				[2]
Total short-term investments				[2]
Total				[2]

[1] Included in cash and cash equivalents in the Company's consolidated balance sheet as of June 30, 2019 in addition to $17.8 million of cash.

[2] Included in cash and cash equivalents in the Company's consolidated balance sheet as of December 31, 2018 in addition to $31.8 million of cash.