Revenue - Contract balances (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Contract balances
Contract assets	$ 4,557	$ 3,075
Contract liabilities	5,483	1,733	$ 1,350
Data analysis
Contract balances
Contract assets	2,411	2,913
Software services
Contract balances
Contract liabilities	2,456
MRM services
Contract balances
Contract assets	1,310
Contract liabilities	1,011
Prescription medications
Contract balances
Contract liabilities	1,049	858
Software maintenance
Contract balances
Contract liabilities	829	730
Health plan management services
Contract balances
Contract assets	836	162
Contract liabilities	$ 138	$ 145