Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2017	Dec. 31, 2017	Jun. 30, 2018
Long-term Purchase Commitment [Line Items]
Prepaid expenses and other current assets		$ 733	$ 560
Prepaid insurance			159
Cost to purchase research and development supplies		100	86
Research and Development Arrangement
Long-term Purchase Commitment [Line Items]
Payments to acquire in-process research and development	$ 245
Prepaid expense			$ 193
Supplies expense		$ 100