Commitments and Contingencies - Leases - Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Apr. 01, 2019
Leases
Right-of-use assets	$ 5,118	$ 5,500
Deferred rent and lease incentive		300
Operating lease liabilities	$ 5,384	$ 5,800
Operating Lease, Liability, Statement of Financial Position		cpst:NotesPayableAndCapitalLeaseObligationsCurrent cpst:NotesPayableAndCapitalLeaseObligationsNoncurrent