BORROWINGS - Long term narrative and interest expense (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
BORROWINGS
Outstanding balance	$ 177,214
Floating interest rate (as a percent)	4.37%	5.43%
Interest expense
Interest capitalized - project assets	$ 10,197	$ 10,794	$ 15,462
Interest capitalized - property, plant, and equipment	154	2,620	1,182
Interest expense	71,874	81,326	106,032
Total interest incurred	82,225	$ 94,740	$ 122,676
Credit facility
BORROWINGS
Maximum borrowing capacity	$ 2,618,761
Unsecured
BORROWINGS
Floating interest rate (as a percent)	3.26%	4.86%
Secured by project assets and solar power systems
BORROWINGS
Floating interest rate (as a percent)	3.63%	3.65%

Contractual floating interest rate for funds borrowed, under the debt agreement.

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Amount of interest costs capitalized for project assets disclosed as an adjusting item to interest costs incurred.

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Amount of interest costs capitalized for property, plant, and equipment disclosed as an adjusting item to interest costs incurred.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Total interest costs incurred during the period and either capitalized or charged against earnings.

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Amount of the cost of borrowed funds accounted for as interest expense.

+ References

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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