Summary of Significant Accounting Policies - Trade Accounts Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Trade Accounts Receivable
Trade accounts receivable	$ 39,004	$ 36,428
Unbilled accounts receivable	4,223	7,577
Trade and unbilled accounts receivable	43,227	44,005
Less allowance for doubtful accounts	(395)	(211)	$ (48)
Accounts receivable, net	$ 42,832	$ 43,794