Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands, shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 24,825	$ 6,754	$ 24,825	$ 6,754	$ 8,116	$ 13,200
Antidilutive securities excluded from the computation of earnings per share (in shares)	3.7	3.7	4.1	4.1