Amount of cash restricted as to withdrawal or usage. 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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=121583591&loc=SL98516268-108586

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1)(a))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(2))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Name:	us-gaap_RestrictedCash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Basis Of Presentation (Details) - USD ($) $ in Millions	Mar. 31, 2021	Feb. 02, 2021	Dec. 31, 2020
Original Senior Unsecured Notes Due 2021 [Member]
Basis Of Presentation [Line Items]
Stated interest rate	7.125%
New Senior Unsecured Notes Due 2021 [Member]
Basis Of Presentation [Line Items]
Stated interest rate	7.125%	7.125%	7.125%
Senior Unsecured Notes Due 2024 [Member]
Basis Of Presentation [Line Items]
Stated interest rate	7.75%	7.75%	7.75%
Creditors Escrow [Member]
Basis Of Presentation [Line Items]
Restricted Cash	$ 16.8
Collateral, Secured Obligations [Member]
Basis Of Presentation [Line Items]
Restricted Cash	77.4
Escrow, Future Decommissioning Obligations [Member]
Basis Of Presentation [Line Items]
Restricted Cash	$ 2.6