Fair Value Measurements - Additional Information (Detail)	3 Months Ended			6 Months Ended
	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Counterparty	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest and dividends	$ 213,000		$ 204,000	$ 381,000	$ 323,000
Mark-to-market gain (loss)	324,000		1,500,000	(798,000)	3,000,000
Impairment on natural gas and oil properties	15,302,000		$ 0	22,614,000	$ 0
Allowance for doubtful accounts on accounts receivable	5,615,000			$ 5,615,000		$ 7,111,000
Number of financial institutions included in counter parties | Counterparty				20
Number of counterparties | Counterparty				5
Net derivative liability	27,500,000			$ 27,500,000
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			$ 0
Impairment on natural gas and oil properties	$ 15,300,000