Fresh start accounting (Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Mar. 21, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 37,446	$ 27,732	$ 45,123
Accounts receivable, net	66,087	60,363	46,837
Inventories, net	4,059	5,138	6,885
Prepaid expenses	2,814	2,661	4,398
Derivative instruments	24,025	0	19,058
Total current assets	134,431	95,894	122,301
Property and equipment, net	43,096	50,641	57,378
Oil and natural gas properties, using the full cost method:
Proved	915,333	634,294	604,065
Unevaluated (excluded from the amortization base)	466,616	482,239	585,574
Accumulated depreciation, depletion, amortization and impairment	(221,431)	(124,180)	0
Total oil and natural gas properties	1,160,518	992,353	1,189,639
Derivative instruments	2,199	0	14,295
Other assets	425	418	8,499
Total assets	1,340,669	1,139,306	1,392,112
Current liabilities:
Accounts payable and accrued liabilities	73,779	75,414	61,676
Accrued payroll and benefits payable	10,976	11,276	9,552
Accrued interest payable	13,359	187	0
Revenue distribution payable	26,225	17,966	11,025
Long-term debt and capital leases, classified as current	3,479	3,273	4,632
Total current liabilities	127,818	117,075	86,885
Long-term debt and capital leases, less current maturities	303,992	141,386	291,429
Deferred compensation	540	696	519
Asset retirement obligations	22,090	33,216	64,216
Liabilities subject to compromise			0
Commitments and contingencies
Stockholders’ equity:
Common stock			450
Additional paid in capital	974,616	961,200	948,613
(Accumulated deficit) retained earnings	(85,460)	(118,902)	0
Total stockholders' equity	884,687	842,766	949,063
Total liabilities and stockholders' equity	$ 1,340,669	$ 1,139,306	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 obligations			0
Liabilities subject to compromise			(1,281,096)
Stockholders’ 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 obligations			(2,757)
Liabilities subject to compromise			0
Stockholders’ 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
Cash and cash equivalents			45,123	$ 186,480	$ 17,065
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 obligations			66,973
Liabilities subject to compromise			1,281,096
Commitments and contingencies
Stockholders’ equity:
Common stock			14
Additional paid in capital			425,425
(Accumulated deficit) retained earnings			(1,437,528)
Total stockholders' equity			(1,012,089)	$ (1,042,153)	$ (620,357)
Total liabilities and stockholders' equity			886,643
Predecessor | Reorganization Adjustments
Stockholders’ equity:
Common stock			(14)
Additional paid in capital			$ (425,425)