Fresh start accounting (Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 21, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 22,595	$ 37,446		$ 45,123
Accounts receivable, net	49,647	66,087		46,837
Inventories, net	3,730	4,059		6,885
Prepaid expenses	3,471	2,814		4,398
Derivative instruments	947	24,025		19,058
Total current assets	80,390	134,431		122,301
Property and equipment, net		43,096		57,378
Oil and natural gas properties, using the full cost method:
Proved	1,276,036	915,333		604,065
Unevaluated (excluded from the amortization base)	371,229	466,616		585,574
Accumulated depreciation, depletion, amortization and impairment	(754,379)	(221,431)		0
Total oil and natural gas properties	892,886	1,160,518		1,189,639
Derivative instruments	0	2,199		14,295
Other assets	635	425		8,499
Total assets	988,432	1,340,669		1,392,112
Current liabilities:
Accounts payable and accrued liabilities	64,558	73,779		61,676
Accrued payroll and benefits payable	10,963	10,976		9,552
Accrued interest payable	12,227	13,359		0
Revenue distribution payable	22,370	26,225		11,025
Long-term debt and capital leases, classified as current	594	12,371		4,632
Total current liabilities	122,669	136,710		86,885
Long-term debt and capital leases, less current maturities	421,392	295,100		291,429
Deferred compensation	165	540		519
Asset retirement obligation	21,073	22,090		64,216
Liabilities subject to compromise				1,281,096
Commitments and contingencies
Stockholders’ (deficit) equity:
Common stock	485	467		450
Additional paid in capital	977,174	974,616		948,613
(Accumulated deficit) retained earnings	(554,408)	(85,460)		0
Total stockholders’ equity	417,141	884,687	$ 842,766	949,063	$ (1,042,153)
Total liabilities and stockholders’ equity	$ 988,432	$ 1,340,669		1,392,112
Reorganization Adjustments
Current assets:
Cash and cash equivalents				(135,333)
Accounts receivable, net				0
Inventories, net				0
Prepaid expenses				(535)
Derivative instruments				0
Total current assets				(135,868)
Property and equipment, net				0
Oil and natural gas properties, using the full cost method:
Proved				0
Unevaluated (excluded from the amortization base)				0
Accumulated depreciation, depletion, amortization and impairment				0
Total oil and natural gas properties				0
Derivative instruments				0
Other assets				2,410
Total assets				(133,458)
Current liabilities:
Accounts payable and accrued liabilities				(2,737)
Accrued payroll and benefits payable				2,186
Accrued interest payable				(2,095)
Revenue distribution payable				3,050
Long-term debt and capital leases, classified as current				(464,182)
Total current liabilities				(463,778)
Long-term debt and capital leases, less current maturities				291,429
Deferred compensation				519
Asset retirement obligation				0
Liabilities subject to compromise				(1,281,096)
Stockholders’ (deficit) equity:
Common stock				450
Additional paid in capital				948,613
(Accumulated deficit) retained earnings				795,844
Total stockholders’ equity				1,319,468
Total liabilities and stockholders’ equity				(133,458)
Fresh Start Adjustments
Current assets:
Cash and cash equivalents				0
Accounts receivable, net				0
Inventories, net				0
Prepaid expenses				0
Derivative instruments				0
Total current assets				0
Property and equipment, net				18,987
Oil and natural gas properties, using the full cost method:
Proved				(3,751,511)
Unevaluated (excluded from the amortization base)				559,535
Accumulated depreciation, depletion, amortization and impairment				3,811,326
Total oil and natural gas properties				619,350
Derivative instruments				0
Other assets				590
Total assets				638,927
Current liabilities:
Accounts payable and accrued liabilities				0
Accrued payroll and benefits payable				0
Accrued interest payable				0
Revenue distribution payable				0
Long-term debt and capital leases, classified as current				0
Total current liabilities				0
Long-term debt and capital leases, less current maturities				0
Deferred compensation				0
Asset retirement obligation				(2,757)
Liabilities subject to compromise				0
Stockholders’ (deficit) equity:
(Accumulated deficit) retained earnings				641,684
Total stockholders’ equity				641,684
Total liabilities and stockholders’ equity				638,927
Predecessor
Current assets:
Cash and cash equivalents				180,456
Accounts receivable, net				46,837
Inventories, net				6,885
Prepaid expenses				4,933
Derivative instruments				19,058
Total current assets				258,169
Property and equipment, net				38,391
Oil and natural gas properties, using the full cost method:
Proved				4,355,576
Unevaluated (excluded from the amortization base)				26,039
Accumulated depreciation, depletion, amortization and impairment				(3,811,326)
Total oil and natural gas properties				570,289
Derivative instruments				14,295
Other assets				5,499
Total assets				886,643
Current liabilities:
Accounts payable and accrued liabilities				64,413
Accrued payroll and benefits payable				7,366
Accrued interest payable				2,095
Revenue distribution payable				7,975
Long-term debt and capital leases, classified as current				468,814
Total current liabilities				550,663
Long-term debt and capital leases, less current maturities				0
Deferred compensation				0
Asset retirement obligation				66,973
Liabilities subject to compromise				1,281,096
Commitments and contingencies
Stockholders’ (deficit) equity:
Common stock				14
Additional paid in capital				425,425
(Accumulated deficit) retained earnings				(1,437,528)
Total stockholders’ equity				(1,012,089)
Total liabilities and stockholders’ equity				886,643
Predecessor | Reorganization Adjustments
Stockholders’ (deficit) equity:
Common stock				(14)
Additional paid in capital				$ (425,425)