Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. 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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Period Type:	instant

Debt - Bonds (Details) - USD ($) $ in Thousands	Jul. 16, 2021	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Debt
Cash and cash equivalents		$ 645,156	$ 405,511	$ 371,854	$ 448,612
Cash and cash equivalents		399,551	405,511
Bond purchase fund		$ 245,605	$ 0
Municipal bonds \| Series 2009 and 2010 Pollution Control Revenue Bonds \| Subsequent Event
Debt
Repayments of pollution control bond	$ 245,600