Leases - Operating lease maturities - Supplemental Information (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 0.8
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Operating Lease, Liability
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Operating Lease, Liability, Current
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Operating Lease, Liability, Noncurrent
Lease assets obtained in exchange for new lease liabilities (non-cash):
Operating	$ 1.6
Finance	$ 0.2
Weighted average items:
Weighted average remaining lease term (in years), Operating leases	3 years 6 months
Weighted average remaining lease term (in years), Finance leases	2 years 4 months 24 days
Weighted average discount rate - operating leases	3.92%
Weighted average discount rate - finance leases	4.06%

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