Significant Accounting Policies - Deferred Revenue (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Deferred revenue	$ 68,557	$ 58,853	$ 34,000
Deferred revenue included in other current liabilities	2,893	2,086
Loans
Disaggregation of Revenue [Line Items]
Deferred revenue	55,406	46,958
PPAs and leases
Disaggregation of Revenue [Line Items]
Deferred revenue	10,151	8,895
SRECs
Disaggregation of Revenue [Line Items]
Deferred revenue	$ 3,000	$ 3,000