Summary of Significant Accounting Policies - Adopted accounting pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total stockholders' equity (deficit)	$ 127,871	$ 122,269	$ (19,829)	$ 25,254	$ (43,010)	$ 57,118	$ 44,534
Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total stockholders' equity (deficit)						$ 2,596
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Average life of contract						12 years 4 months 24 days
Accounting Standards Update 2014-09 | Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total stockholders' equity (deficit)						$ 2,600