Revenue - Contract balances (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Contract balances
Contract assets	$ 6,168	$ 3,075
Contract liabilities	4,667	1,733	$ 1,350
Data analysis
Contract balances
Contract assets	4,267	2,913
Software services
Contract balances
Contract liabilities	1,735
Prescription medications
Contract balances
Contract liabilities	1,395	858
Software maintenance
Contract balances
Contract liabilities	765	730
MRM services
Contract balances
Contract assets	984
Contract liabilities	602
Health plan management services
Contract balances
Contract assets	917	162
Contract liabilities	$ 170	$ 145