Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) Customer Segment	Dec. 31, 2018 USD ($) Customer	Dec. 31, 2017 USD ($) Customer
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable	$ 77,402	$ 119,332
Depreciation, depletion, amortization and accretion	$ 156,552	134,940	$ 119,362
Number of operating segment | Segment	1
Amortization of deferred financing costs and debt discount	$ 4,100	3,600	3,400
Oil and Gas Properties [Member]
Summary Of Significant Accounting Policies [Line Items]
Depreciation, depletion, amortization and accretion	153,800	133,200	117,300
Other property and equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Depreciation	$ 2,200	1,800	2,000
Other property and equipment [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, expected lives	5 years
Other property and equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, expected lives	40 years
Proved Oil And Gas Properties [Member] | Marcellus Shale [Member]
Summary Of Significant Accounting Policies [Line Items]
Impairment of oil and gas properties	$ 0	0	0
Unproved Oil And Gas Properties [Member]
Summary Of Significant Accounting Policies [Line Items]
Impairment of oil and gas properties	45,800	27,600	$ 28,300
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member]
Summary Of Significant Accounting Policies [Line Items]
Fair value of commodity derivative contracts	$ 27,100	$ 5,700
Sales Revenue, Net [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of customers | Customer	2	1	2
Revenue From Contract With Customer [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable	$ 63,700	$ 94,100