Commitments - Separation Agreement (Details) $ in Thousands	Sep. 12, 2017 USD ($) installment shares	Sep. 05, 2017	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Other Commitments [Line Items]
Accrued salaries and wages			$ 643	$ 713
Separation Agreement
Other Commitments [Line Items]
Expiration period of resignation revocation		7 days
Payments for accrued obligations	$ 1,130
Other commitments, payment period	3 days
Payments for postemployment benefits	$ 1,440
Options granted (in shares) | shares	948,000
Maximum period of advisement by former officer	12 months
Accrued salaries and wages			$ 962
Separation Agreement | Minimum
Other Commitments [Line Items]
Number of installment payments | installment	1
Separation Agreement | Maximum
Other Commitments [Line Items]
Number of installment payments | installment	2