LONG-TERM DEBT - Revolving credit agreement (Details)											12 Months Ended		17 Months Ended
	Jun. 05, 2020 USD ($)	Apr. 21, 2020 USD ($)	Apr. 14, 2020 USD ($)	Mar. 30, 2020 USD ($)	Feb. 28, 2020 USD ($)	Feb. 24, 2020 USD ($)	Nov. 27, 2019	Sep. 30, 2019 USD ($)	May 06, 2019 USD ($) day	Oct. 10, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Feb. 28, 2020 USD ($)	Feb. 14, 2020 installment	Feb. 06, 2020 installment	Jan. 17, 2020 USD ($) installment	Nov. 05, 2019	Oct. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)	Jul. 26, 2019 USD ($)	Mar. 05, 2019 USD ($)	Mar. 04, 2019 USD ($)
Debt Instrument [Line Items]
Long-term debt											$ 115,000,000	$ 157,804,000
Amortization of debt financing costs											$ 803,000	3,241,000
Ratio of total debt to EBITDAX (not more than)										400.00%
Ratio of current assets to current liabilities (not less than)										100.00%
Percentage of production required to be maintained (not less than)											75.00%
Minimum period of swap agreements maintained											24 months
Cash and cash equivalents											$ 3,753,000	21,137,000
Repayments of lines of credit											18,000,000	0
Revolving Credit Facility
Debt Instrument [Line Items]
Agreement term										5 years
Line of credit facility, maximum borrowing capacity										$ 500,000,000.0
Line of credit facility, borrowing base										$ 95,000,000.0		108,000,000.0							$ 115,000,000.0	$ 115,000,000	$ 125,000,000	$ 108,000,000
Line of credit facility, commitment fee percentage										0.50%
Ratio of current assets to current liabilities (not less than)								85.00%		100.00%
Percentage of production required to be maintained (not less than)																				75.00%
Percentage of net cash proceeds from dispositions used to repay borrowings																	100.00%
Covenant, borrowing base deficiency, repayment in full, period after redetermination										30 days
Covenant, borrowing base deficiency, monthly installment repayment period							4 months			6 months
Covenant, borrowing base deficiency, monthly installment repayment, period after redetermination							30 days			30 days
Letter of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity											5,000,000.0
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt											115,000,000	75,000,000						$ 115,000,000
Amortization of debt financing costs											$ 800,000	2,200,000
Option to effect repayment, in full, period after redetermination										30 days
Option to effect repayment, monthly installments, period after redetermination										6 months
Ratio of total debt to EBITDAX (not more than)									300.00%	400.00%
Ratio of current assets to current liabilities (not less than)										100.00%
Basis spread									0.25%
Period of consecutive business days (at least) | day									5
Line of Credit | Minimum | Revolving Credit Facility
Debt Instrument [Line Items]
Cash and cash equivalents									$ 10,000,000
Other Current Assets | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Unamortized debt issuance costs								$ 2,600,000				500,000
Other Noncurrent Assets | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Unamortized debt issuance costs												$ 1,700,000
Subsequent Event
Debt Instrument [Line Items]
Repayments of lines of credit													$ 17,300,000
Subsequent Event | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, borrowing base																$ 90,000,000
Borrowing base deficiency																$ 25,000,000
Covenant, borrowing base deficiency, number of equal monthly installments (in installments) | installment														2		4
Covenant, borrowing base deficiency, equal monthly installment, amount						$ 6,250,000
Covenant, borrowing base deficiency, number of subsequent monthly installments (in installments) | installment														2	2
Repayments of lines of credit			$ 1,500,000	$ 1,500,000
Extension term				45 days
Subsequent Event | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, borrowing base																$ 90,000,000.0
Borrowing base deficiency																$ 25,000,000
Installment payment		$ 7,750,000			$ 17,300,000
Forecast
Debt Instrument [Line Items]
Repayments of lines of credit	$ 7,800,000
Forecast | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Borrowing base deficiency	7,800,000
Installment payment	$ 7,750,000