Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) £ in Thousands, $ in Thousands	Jun. 30, 2018 USD ($)	Jun. 30, 2018 GBP (£)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 11,245		$ 8,116	$ 7,595	$ 13,200
Cash, FDIC Insured Amount	$ 250
Cash, FSCS Insured Amount | £		£ 85