Fair Value Measurements - Additional Information (Detail)	3 Months Ended				9 Months Ended
	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Counterparty	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest and dividends	$ 225,000			$ 1,500,000	$ 606,000	$ 2,400,000
Mark-to-market gain	1,300,000			1,100,000	522,000	4,100,000
Impairment on natural gas and oil properties	0			63,679,000	22,614,000	$ 63,679,000
Allowance for doubtful accounts on accounts receivable	5,862,000				$ 5,862,000		$ 7,111,000
Number of financial institutions included in counter parties | Counterparty					21
Number of counterparties | Counterparty					5
Net derivative liability	$ 23,900,000				$ 23,900,000
Oklahoma
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment on natural gas and oil properties			$ 7,300,000
Northwest Pennsylvania
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value		$ 0
Impairment on natural gas and oil properties		$ 15,300,000
Oklahoma And Texas Panhandle
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment on natural gas and oil properties				$ 63,700,000