4. Restricted Marketable Securities (Details) - Restricted Marketable Securities - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	$ 253,236		$ 223,785
Restricted cash - noncurrent	$ 43,805		80,072
Product minimum service life	25 years
Gains on sales of marketable securities and restricted marketable securities	$ 15,337	$ 15,016
Cash Held In Trust [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted cash - noncurrent	700		100
Restricted Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	253,236		223,785
Proceeds from sale of restricted marketable securities	115,200	47,900
Gains on sales of marketable securities and restricted marketable securities	15,100	15,000
Payments to Acquire Restricted Marketable Securities	114,500
Proceeds from sale of restricted marketable securities withdrawn from custodial accounts		$ 14,900
Restricted Debt Securities [Member] \| Foreign government obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	132,883		126,066
Restricted Debt Securities [Member] \| US Government Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	$ 120,353		$ 97,719

Proceeds from sale of restricted investments withdrawn from custodial accounts

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Describes the solar modules minimum service life.

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- Definition

Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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The cash outflow to acquire investments (not to include restricted cash) that are pledged or subject to withdrawal restrictions.

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The cash inflow associated with the sale of investments that are pledged or subject to withdrawal restrictions during the period.

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Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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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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