Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Other comprehensive income, tax	$ 0	$ 0	$ 0

Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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+ Details