Summary of Significant Accounting Policies - Additional Information (Detail)		3 Months Ended								12 Months Ended
		Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) Counterparty Customer	Dec. 31, 2018 USD ($) Customer	Dec. 31, 2017 USD ($) Customer	Dec. 31, 2015 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Net brokered margin gain (loss)										$ (14,200,000)	$ (16,300,000)	$ (5,700,000)
Allowance for doubtful accounts on accounts receivable		$ 8,784,000				$ 6,118,000				8,784,000	6,118,000
Bad debt (income) expense										4,341,000	(1,000,000)	1,550,000
Net book value of unproved properties	[1]	868,180,000				2,110,277,000				868,180,000	2,110,277,000	2,644,000,000
Abandonment and impairment of unproved properties		1,193,711,000	$ 16,202,000	$ 12,770,000	$ 12,659,000	441,750,000	$ 6,549,000	$ 54,922,000	$ 11,773,000	1,235,342,000	514,994,000	269,725,000
Depreciation expense										$ 5,000,000.0	6,000,000.0	$ 7,700,000
Lease, practical expedients, package [true false]										true
Marketable securities held in deferred compensation plans		62,000,000.0				57,300,000				$ 62,000,000.0	57,300,000
Other investments including surface acreage		9,600,000				$ 9,100,000				$ 9,600,000	$ 9,100,000
Number of customers accounted more than 10% of total oil and gas revenues | Customer										1	1	1
Number of counterparties | Counterparty										3
Number of financial institutions included in counter parties | Counterparty										20
Number of counterparties amount payable | Counterparty										1
Number of counterparties amount receivable | Counterparty										2
Counterparties not in Facility
Summary Of Significant Accounting Policies [Line Items]
Net derivative liability		6,700,000								$ 6,700,000
One Counterparty
Summary Of Significant Accounting Policies [Line Items]
Net derivative liability		12,600,000								12,600,000
Two Counterparties
Summary Of Significant Accounting Policies [Line Items]
Derivative amount receivable		$ 5,900,000								$ 5,900,000
Maximum
Summary Of Significant Accounting Policies [Line Items]
Short-term leases initial term										1 year
Lessee, operating lease, contract term		1 month								1 month
Pennsylvania
Summary Of Significant Accounting Policies [Line Items]
Net book value of unproved properties		$ 868,200,000								$ 868,200,000
North Louisiana
Summary Of Significant Accounting Policies [Line Items]
Abandonment and impairment of unproved properties										1,200,000,000	$ 436,000,000.0
Natural Gas and Oil Properties | Northwest Pennsylvania
Summary Of Significant Accounting Policies [Line Items]
Fair Value													$ 0
Adjustments of the asset retirement liability additional expense										$ 213,000	$ 9,800,000	$ 158,000
Other property and equipment | Minimum
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets										3 years
Other property and equipment | Maximum
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets										10 years
Office Space
Summary Of Significant Accounting Policies [Line Items]
Lessee, operating sublease, option to terminate										All of our subleases have terms that end in 2020 or 2022. The sublease agreements are non-cancelable through the end of the term and both parties have substantive rights to terminate the lease when the term is complete.
Expected subleases through beginning of 2022		$ 3,100,000								$ 3,100,000
Office Space | Minimum
Summary Of Significant Accounting Policies [Line Items]
Lessee, operating lease, contract term		1 year								1 year
Office Space | Maximum
Summary Of Significant Accounting Policies [Line Items]
Lessee, operating lease, contract term		15 years								15 years
Field Equipment
Summary Of Significant Accounting Policies [Line Items]
Lessee, Operating Lease, Option to Extend										Our compressor and cooler arrangements are typically structured with a non-cancelable primary term of one to two years and continue thereafter on a month-to-month basis subject to termination by either party with thirty days notice.
Lessee Operating Lease Notice Period for Renewal										30 days
Field Equipment | Minimum
Summary Of Significant Accounting Policies [Line Items]
Lessee, operating lease, contract term		1 year								1 year
Field Equipment | Maximum
Summary Of Significant Accounting Policies [Line Items]
Lessee, operating lease, contract term		2 years								2 years
Vehicle Fleet
Summary Of Significant Accounting Policies [Line Items]
Lessee Operating Lease Notice Period for Renewal										3 years
Lessee operating lease contract of team description										Our vehicle agreements are non-cancelable for a minimum term of one year and a maximum term of four to eight years depending on the type of vehicle. However, we have assumed a term of three years based on the period covered by options to terminate that we are reasonably certain to exercise.
Vehicle Fleet | Minimum
Summary Of Significant Accounting Policies [Line Items]
Lessee, operating lease, contract term		1 year								1 year
Lessee, operating lease, non-cancelable maximum contract term, depending on type of vehicle										4 years
Vehicle Fleet | Maximum
Summary Of Significant Accounting Policies [Line Items]
Lessee, operating lease, non-cancelable maximum contract term, depending on type of vehicle										8 years
Other Equipment
Summary Of Significant Accounting Policies [Line Items]
Lessee, operating lease, contract term		18 months								18 months
Lessee, Operating Lease, Option to Extend										This arrangement is structured with a non-cancellable primary term of eighteen months, with two optional extension periods of six months
Lessee, operating lease, option to extend										true
Lessee, operating lease, option to extend, term										6 months
Lessee, operating lease, existence of option to terminate										true

[1] Includes capitalized asset retirement costs and the associated accumulated amortization.