Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 19,636	$ 16,564	$ 18,216	$ 13,622	$ 19,656	$ 13,478	$ 12,430	$ 9,601	$ 68,038	$ 55,165	$ 43,799
Percent of total revenue									100.00%
Net Basis
Disaggregation of Revenue [Line Items]
Revenue									$ 58,457
Percent of total revenue									86.00%
Gross Basis
Disaggregation of Revenue [Line Items]
Revenue									$ 9,582
Percent of total revenue									14.00%