Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 525,488	$ 142,340	$ 75,293	$ 458,956
Restricted cash	75,005	0
Accounts receivable—oil and gas	86,621	103,858
Accounts receivable - related parties	90	46
Accounts receivable - intercompany		0
Prepaid expenses and other current assets	15,168	3,714
Short-term derivative instruments	77,350	78,391
Total current assets	779,722	328,349
Property and equipment:
Oil and natural gas properties	4,798,835	3,923,154
Other property and equipment	22,930	18,344
Accumulated depletion, depreciation, amortization and impairment	(1,211,308)	(1,050,879)
Property and equipment, net	3,610,457	2,890,619
Other assets:
Equity investments and investments in subsidiaries	362,391	369,581
Derivative instruments	25,871	24,448
Other assets	25,418	19,396
Total other assets	413,680	413,425
Total assets	4,803,859	3,632,393
Current liabilities:
Accounts payable and accrued liabilities	318,725	371,410
Accounts payable - intercompany	0	0
Asset retirement obligation—current	75	75	795
Short-term derivative instruments	937
Deferred tax liability - current	26,508	27,070
Current maturities of long-term debt	1,738	168
Total current liabilities	347,983	398,723
Long-term derivative instrument	2,753	0
Asset retirement obligation—long-term	21,202	17,863	15,181
Deferred tax liability	201,022	203,195
Long-term debt, net of current maturities	963,593	716,316
Total liabilities	1,536,553	1,336,097
Stockholders’ equity:
Common stock	1,081	856
Paid-in capital	2,816,930	1,828,602
Accumulated other comprehensive income (loss)	(38,412)	(26,675)
Retained earnings (accumulated deficit)	487,707	493,513
Total stockholders’ equity	3,267,306	2,296,296	2,188,499	2,050,238
Total liabilities and stockholders’ equity	4,803,859	3,632,393
Parent [Member]
Current assets:
Cash and cash equivalents	524,240	141,535	72,921	451,431
Restricted cash	75,005
Accounts receivable—oil and gas	86,558	103,762
Accounts receivable - related parties	90	46
Accounts receivable - intercompany	48,401	45,222
Prepaid expenses and other current assets	15,168	3,714
Short-term derivative instruments	77,350	78,391
Total current assets	826,812	372,670
Property and equipment:
Oil and natural gas properties	4,760,793	3,887,874
Other property and equipment	22,887	18,301
Accumulated depletion, depreciation, amortization and impairment	(1,211,281)	(1,050,855)
Property and equipment, net	3,572,399	2,855,320
Other assets:
Equity investments and investments in subsidiaries	353,243	360,238
Derivative instruments	25,871	24,448
Other assets	25,418	19,396
Total other assets	404,532	404,082
Total assets	4,803,743	3,632,072
Current liabilities:
Accounts payable and accrued liabilities	318,609	371,089
Accounts payable - intercompany	0	0
Asset retirement obligation—current	75	75
Short-term derivative instruments	937
Deferred tax liability - current	26,508	27,070
Current maturities of long-term debt	1,738	168
Total current liabilities	347,867	398,402
Long-term derivative instrument	2,753
Asset retirement obligation—long-term	21,202	17,863
Deferred tax liability	201,022	203,195
Long-term debt, net of current maturities	963,593	716,316
Total liabilities	1,536,437	1,335,776
Stockholders’ equity:
Common stock	1,081	856
Paid-in capital	2,816,930	1,828,602
Accumulated other comprehensive income (loss)	(38,412)	(26,675)
Retained earnings (accumulated deficit)	487,707	493,513
Total stockholders’ equity	3,267,306	2,296,296
Total liabilities and stockholders’ equity	4,803,743	3,632,072
Guarantors [Member]
Current assets:
Cash and cash equivalents	1,247	804	2,371	7,525
Accounts receivable—oil and gas	63	96
Accounts receivable - related parties	0	0
Accounts receivable - intercompany	55	27
Prepaid expenses and other current assets		0
Short-term derivative instruments	0	0
Total current assets	1,365	927
Property and equipment:
Oil and natural gas properties	38,771	35,990
Other property and equipment	43	43
Accumulated depletion, depreciation, amortization and impairment	(27)	(24)
Property and equipment, net	38,787	36,009
Other assets:
Equity investments and investments in subsidiaries		0
Derivative instruments	0	0
Other assets		0
Total assets	40,152	36,936
Current liabilities:
Accounts payable and accrued liabilities	116	321
Accounts payable - intercompany	48,326	45,143
Asset retirement obligation—current		0
Deferred tax liability - current		0
Current maturities of long-term debt		0
Total current liabilities	48,442	45,464
Long-term derivative instrument	0
Asset retirement obligation—long-term	0	0
Deferred tax liability		0
Long-term debt, net of current maturities	0	0
Total liabilities	48,442	45,464
Stockholders’ equity:
Common stock		0
Paid-in capital	322	322
Accumulated other comprehensive income (loss)		0
Retained earnings (accumulated deficit)	(8,612)	(8,850)
Total stockholders’ equity	(8,290)	(8,528)
Total liabilities and stockholders’ equity	40,152	36,936
Non-Guarantor [Member]
Current assets:
Cash and cash equivalents	1	1	1	0
Restricted cash	0
Accounts receivable—oil and gas	0	0
Accounts receivable - related parties	0	0
Accounts receivable - intercompany	0	0
Prepaid expenses and other current assets	0	0
Short-term derivative instruments	0	0
Total current assets	1	1
Property and equipment:
Oil and natural gas properties		0
Other property and equipment		0
Accumulated depletion, depreciation, amortization and impairment		0
Property and equipment, net		0
Other assets:
Equity investments and investments in subsidiaries	164,112	180,217
Derivative instruments	0	0
Other assets		0
Total other assets	164,112	180,217
Total assets	164,113	180,218
Current liabilities:
Accounts payable and accrued liabilities		0
Accounts payable - intercompany	130	106
Asset retirement obligation—current		0
Deferred tax liability - current		0
Current maturities of long-term debt		0
Total current liabilities	130	106
Long-term derivative instrument	0
Asset retirement obligation—long-term	0	0
Deferred tax liability		0
Long-term debt, net of current maturities	0	0
Total liabilities	130	106
Stockholders’ equity:
Common stock		0
Paid-in capital	235,347	227,079
Accumulated other comprehensive income (loss)	(38,412)	(26,675)
Retained earnings (accumulated deficit)	(32,952)	(20,292)
Total stockholders’ equity	163,983	180,112
Total liabilities and stockholders’ equity	164,113	180,218
Eliminations [Member]
Current assets:
Cash and cash equivalents	0	0	$ 0	$ 0
Restricted cash	0
Accounts receivable—oil and gas		0
Accounts receivable - related parties	0	0
Accounts receivable - intercompany	(48,456)	(45,249)
Prepaid expenses and other current assets		0
Short-term derivative instruments	0	0
Total current assets	(48,456)	(45,249)
Property and equipment:
Oil and natural gas properties	(729)	(710)
Other property and equipment		0
Accumulated depletion, depreciation, amortization and impairment		0
Property and equipment, net	(729)	(710)
Other assets:
Equity investments and investments in subsidiaries	(154,964)	(170,874)
Derivative instruments	0	0
Other assets		0
Total other assets	(154,964)	(170,874)
Total assets	(204,149)	(216,833)
Current liabilities:
Accounts payable and accrued liabilities		0
Accounts payable - intercompany	(48,456)	(45,249)
Asset retirement obligation—current		0
Deferred tax liability - current		0
Current maturities of long-term debt		0
Total current liabilities	(48,456)	(45,249)
Long-term derivative instrument	0
Asset retirement obligation—long-term	0	0
Deferred tax liability		0
Long-term debt, net of current maturities	0	0
Total liabilities	(48,456)	(45,249)
Stockholders’ equity:
Common stock		0
Paid-in capital	(235,669)	(227,401)
Accumulated other comprehensive income (loss)	38,412	26,675
Retained earnings (accumulated deficit)	41,564	29,142
Total stockholders’ equity	(155,693)	(171,584)
Total liabilities and stockholders’ equity	$ (204,149)	$ (216,833)