Significant Accounting Policies (Royalty Interests in Oil and Natural Gas Properties) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
Dec. 31, 2020	Nov. 30, 2020	Aug. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Acquisition of mineral and royalty interest	$ 12,000	$ 2,000	$ 200	$ 14,181	$ 0

The cash outflow from the acquisition of a mineral right which is the right to extract a mineral from the earth or to receive payment, in the form of royalty, for the extraction of minerals.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

Name:	us-gaap_PaymentsToAcquireMineralRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration