Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest and dividends					$ 1,100,000	$ 4,100,000	$ 972,000
Mark-to-market gain (loss)					$ (7,900,000)	4,200,000	3,100,000
Closing stock price	$ 9.57				$ 9.57
Impairment of goodwill	$ 1,641,197,000	$ 0	$ 0	$ 0	$ 1,641,197,000	0	0
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				$ 7,300,000	$ 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
Western Oklahoma
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment on natural gas and oil properties							$ 43,000,000