Acquisitions and Divestitures (Details)				1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
		Jul. 31, 2018 USD ($)	Mar. 01, 2018 USD ($)	Nov. 30, 2018 USD ($)	Jul. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($) a $ / shares	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2018 USD ($) a $ / shares	Sep. 30, 2017 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Feb. 28, 2018 USD ($)	Nov. 01, 2017 USD ($)	Sep. 29, 2017 USD ($) a
Business Acquisition [Line Items]
Cash Received for Suspended Revenues Attributable to Acquired Properties			$ 355,000
Business Acquisition, Transaction Costs							$ 500,000		$ 500,000
Capitalized Costs, Proved Properties							2,400,000	$ 1,600,000	2,400,000	$ 1,600,000
Asset Retirement Obligation							3,800,000		3,800,000
Proceeds from sales of assets, net									1,700,000
Earnest Money Deposits	[1]						0		0		$ 3,210,000
Business Acquisition, Pro Forma Revenue							127,185,000	48,174,000	321,221,000	147,873,000
Property, Plant and Equipment, Gross							1,015,703,000		1,015,703,000		590,375,000
Amount Transferred from Escrow Account												$ 2,500,000
Escrow Distributed												$ 700,000
Amount Transferred from Escrow Account														$ 7,100,000
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax							$ 16,276,000	$ (6,939,000)	$ 27,144,000	$ 44,051,000
Business Acquisition, Pro Forma Earnings Per Share, Basic | $ / shares							$ 1.08	$ (0.46)	$ 1.80	$ 2.94
Business Acquisition, Pro Forma Earnings Per Share, Diluted | $ / shares							$ 1.06	$ (0.46)	$ 1.78	$ 2.92
Second Lien Facility							$ 200,000,000		$ 200,000,000		200,000,000			200,000,000
Hunt Acquisition [Member]
Business Acquisition [Line Items]
Other Payments to Acquire Businesses									$ 86,000,000
Cash Paid on Date of Acquisition			84,400,000
Cash Paid on Date of Acquisition			82,955,000
Accumulated Costs, net of suspended revenues, for wells in which Hunt elected not to participate			13,778,000
Acreage, Net | a							9,700		9,700
Working Capital Adjustments, Net		$ (200,000)			$ (200,000)		$ (245,000)		$ (245,000)
Cash Received for Suspended Revenues Attributable to Acquired Properties					1,448,000
Business Acquisition, Transaction Costs			96,978,000			$ 400,000					100,000
Capitalized Costs, Proved Properties			82,443,000
Capitalized Costs, Unproved Properties			16,339,000
Asset Retirement Obligation			356,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net			96,978,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual						400,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual						$ 200,000
Devon Acquisition [Member]
Business Acquisition [Line Items]
Other Payments to Acquire Businesses											205,000,000
Cash Paid on Date of Acquisition			190,277,000											$ 189,900,000
Acreage, Net | a														19,600
Working Capital Adjustments, Net			(2,451,000)
Cash Received for Suspended Revenues Attributable to Acquired Properties									400,000
Business Acquisition, Transaction Costs														$ 1,000,000
Capitalized Costs, Proved Properties			42,866,000
Capitalized Costs, Unproved Properties			146,686,000
Asset Retirement Obligation			494,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net			197,345,000
Escrow Deposit														$ 10,300,000
Earnest Money Deposits											$ 3,200,000
Additional working interests													$ 700,000
Property, Plant and Equipment, Gross			8,642,000
Amount Transferred from Escrow Account			9,519,000
Preliminary Purchase Price			$ 197,345,000
Mid-Continent Divestiture [Member]
Business Acquisition [Line Items]
Working Capital Adjustments, Net		1,300,000			$ 1,300,000
Asset Retirement Obligation							300,000		300,000
Proceeds from sales of assets, net		$ 6,200,000							6,000,000
Pre-Tax Operating Income Attributable to Assets Sold							$ (200,000)	$ (900,000)	$ (1,600,000)	$ (1,500,000)
Subsequent Event [Member] | Mid-Continent Divestiture [Member]
Business Acquisition [Line Items]
Cash Paid to Buyer in Connection with Final Settlement				$ 500,000
Cash Paid for Suspended Revenues in Connection with FInal Settlement				$ 200,000

[1] Represents the amount remaining in the Escrow Account for the Devon Acquisition, which was utilized to fund the remaining liabilities due to Devon for the final settlement in March 2018 (see Note 3).