Subsequent Events - Additional Information (Detail) - Subsequent Event - Northwest Pennsylvania $ in Millions	Jul. 15, 2019 USD ($) a Agreement
Subsequent Event [Line Items]
Number of agreements closed \| Agreement	2
Percentage of royalty disposed	2.00%
Proceeds from royalties \| $	$ 600.0
Properties encompass net surface acreage \| a	350,000

Cash received for royalties during the current period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3536-108585

Name:	us-gaap_ProceedsFromRoyaltiesReceived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration