Long-Term Debt (Details) $ in Thousands									3 Months Ended			6 Months Ended	9 Months Ended		12 Months Ended
		Jan. 01, 2017	Nov. 02, 2015 USD ($)	Sep. 30, 2015 USD ($)	May. 01, 2015 USD ($)	Oct. 03, 2012 USD ($)	Nov. 25, 2009 USD ($)	Jun. 01, 2007 USD ($)	Dec. 31, 2016	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2016	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2016	Feb. 01, 2016	Dec. 31, 2014 USD ($)	Nov. 30, 2011 USD ($)
Bank Borrowings
Outstanding bank borrowings under credit facility	[1]			$ 1,179,132						$ 1,179,132			$ 1,179,132				$ 1,074,534
Capitalized interest on our unproved properties										1,200	$ 1,200		3,600	$ 3,700
Interest expense including amortization of debt issuance costs										19,438	18,197		56,407	55,295
Senior Notes [Member] | Senior Notes Due 2017 [Member]
Bank Borrowings
Outstanding bank borrowings under credit facility				250,000						250,000			250,000				250,000
Long-term Debt, Maturities, Repayments of Principal in Year Three				250,000						250,000			250,000
Interest expense including amortization of debt issuance costs										4,600	4,600		13,700	13,700
Senior Notes
Senior notes, issued								$ 250,000
Debt instrument, interest rate, stated percentage								7.125%
Percentage at which senior notes are issued, of par value								100.00%
Debt Issuance Cost				900				$ 4,200
Holder right to require company to repurchase notes at purchase price in cash								101.00%
Senior Notes [Member] | Senior Notes Due 2020 [Member]
Bank Borrowings
Outstanding bank borrowings under credit facility	[1]			223,043						223,043			223,043				222,775
Long-term Debt, Maturities, Repayments of Principal after Year Five				225,000						225,000			225,000
Interest expense including amortization of debt issuance costs										5,200	5,200		15,600	15,600
Senior Notes
Senior notes, issued							$ 225,000
Debt instrument, interest rate, stated percentage							8.875%
Original unamortized issuance discount on senior notes							$ 3,600
Percentage at which senior notes are issued, of par value							98.389%
Effective Interest Rate On Senior Notes Including Discount							9.125%
Debt Issuance Cost				2,700			$ 5,000
Holder right to require company to repurchase notes at purchase price in cash							101.00%
Senior Notes [Member] | Senior Notes Due 2022 [Member]
Bank Borrowings
Outstanding bank borrowings under credit facility	[1]			404,089						404,089			404,089				404,459
Long-term Debt, Maturities, Repayments of Principal after Year Five				400,000						400,000			400,000
Interest expense including amortization of debt issuance costs										$ 7,900	7,900		23,700	23,700
Senior Notes
Senior notes, issued						$ 400,000												$ 250,000
Debt instrument, interest rate, stated percentage						7.875%
Original unamortized issuance discount on senior notes																		$ 2,100
Percentage at which senior notes are issued, of par value																		99.156%
Effective Interest Rate On Senior Notes Including Discount																		8.00%
Percentage of maximum redemption of principal amount of notes						35.00%
Redemption of Debts with Net Proceeds of Qualifying Offerings at Price Above Principle Amount of Debts						107.875%
Debt Issuance Cost				5,400		$ 7,500
Holder right to require company to repurchase notes at purchase price in cash						101.00%
Senior Notes [Member] | Additional Senior Notes Due 2022 [Member]
Senior Notes
Senior notes, issued						$ 150,000
Percentage at which senior notes are issued, of par value						105.00%
Effective Interest Rate On Senior Notes Including Discount						6.993%
Debt Instrument, Unamortized Premium						$ 7,500
Line of Credit [Member]
Bank Borrowings
Line of credit, required security interest on oil and gas properties										75.00%
Outstanding bank borrowings under credit facility				302,000						$ 302,000			302,000				$ 197,300
Line of Credit Facility, current borrowing capacity					$ 375,000
Line of Credit, current commitment amount					$ 375,000
Percentage of applicable margin with federal fund rate										0.50%
Percentage of applicable margin with LIBOR										1.00%
Lead bank's prime rate										3.25%
Commitment fee basis points for the credit facility										0.50%
Maximum level of cash dividends in any fiscal year				15,000						$ 15,000			15,000
Equity Restrictions				$ 50,000						50,000			$ 50,000
Line of credit, covenant, working capital ratio, minimum				1.0
Debt instrument, covenant, working capital ratio, company actual				1.3
Debt instrument, covenant, interest coverage ratio, minimum													1.5
Debt instrument, covenant, interest coverage ratio, company actual													2.1
Line of Credit, covenant, senior secured leverage ratio, minimum													3.0
Line of Credit, covenant, senior secured severage ratio, company actual													2.0
Line of Credit, covenant, liquidity requirement					15.00%
Interest expense including amortization of debt issuance costs										2,300	1,700		$ 6,300	5,900
Commitment fees included in interest expense, net										$ 100	$ 200		$ 500	$ 600
Senior Notes
Debt Issuance Cost				$ 2,000
Line of Credit [Member] | Minimum [Member] | Alternative Base Interest Rate [Member]
Bank Borrowings
Debt instrument escalating basis spread on base rate										75
Line of Credit [Member] | Minimum [Member] | Eurodollar Interest Rate [Member]
Bank Borrowings
Debt Instrument Escalating Rates for Eurodollar Rate Loans										175
Line of Credit [Member] | Maximum [Member] | Alternative Base Interest Rate [Member]
Bank Borrowings
Debt instrument escalating basis spread on base rate										175
Line of Credit [Member] | Maximum [Member] | Eurodollar Interest Rate [Member]
Bank Borrowings
Debt Instrument Escalating Rates for Eurodollar Rate Loans										275
Debt Instrument, Redemption, Period One [Member] | Senior Notes [Member] | Senior Notes Due 2017 [Member]
Senior Notes
Debt Instrument, Redemption Price, Percentage								100.00%
Debt Instrument, Redemption, Period One [Member] | Senior Notes [Member] | Senior Notes Due 2020 [Member]
Senior Notes
Debt Instrument, Redemption Price, Percentage							104.438%
Debt Instrument, Redemption, Period One [Member] | Senior Notes [Member] | Senior Notes Due 2022 [Member]
Senior Notes
Debt Instrument, Redemption Price, Percentage						103.938%
Debt Instrument, Redemption, Period Two [Member] | Senior Notes [Member] | Senior Notes Due 2020 [Member]
Senior Notes
Debt Instrument, Redemption Price, Percentage							100.00%
Debt Instrument, Redemption, Period Two [Member] | Senior Notes [Member] | Senior Notes Due 2022 [Member]
Senior Notes
Debt Instrument, Redemption Price, Percentage						100.00%
Subsequent Event [Member] | Line of Credit [Member]
Bank Borrowings
Line of credit, required security interest on oil and gas properties			95.00%
Line of Credit Facility, current borrowing capacity			$ 330,000
Line of Credit, current commitment amount			$ 330,000
Line of credit, covenant, working capital ratio, minimum		1.0													0.5
Debt instrument, covenant, interest coverage ratio, minimum		2.0							1.30			1.15
Line of Credit, covenant, senior secured leverage ratio, minimum		2.50							3.0			3.50
Senior Notes
Debt Instrument, Borrowing Base Redetermination Acceleration Clause																50.00%
Subsequent Event [Member] | Line of Credit [Member] | Minimum [Member] | Alternative Base Interest Rate [Member]
Bank Borrowings
Debt instrument escalating basis spread on base rate			100
Subsequent Event [Member] | Line of Credit [Member] | Minimum [Member] | Eurodollar Interest Rate [Member]
Bank Borrowings
Debt Instrument Escalating Rates for Eurodollar Rate Loans			200
Subsequent Event [Member] | Line of Credit [Member] | Maximum [Member] | Alternative Base Interest Rate [Member]
Bank Borrowings
Debt instrument escalating basis spread on base rate			200
Subsequent Event [Member] | Line of Credit [Member] | Maximum [Member] | Eurodollar Interest Rate [Member]
Bank Borrowings
Debt Instrument Escalating Rates for Eurodollar Rate Loans			300

[1] Amounts are shown net of any debt discount or premium