Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 95,466	$ 167,088	$ 12,280	$ 93,897
Accounts receivable—oil and gas	47,673	25,615
Accounts receivable-related parties	29,797	34,848
Accounts receivable - intercompany		0
Prepaid expenses and other current assets	4,634	1,506
Deferred tax asset	787	0
Short-term derivative instruments	1,633	664
Note receivable - related party	875	0
Total current assets	180,865	229,721
Property and equipment:
Oil and natural gas properties, full-cost accounting	2,253,605	1,611,090
Other property and equipment	10,164	8,662
Accumulated depletion, depreciation, amortization and impairment	(747,698)	(665,884)
Property and equipment, net	1,516,071	953,868
Other assets:
Equity investments	500,679	381,484
Derivative instruments	127	0
Other assets	12,827	13,295
Total other assets	513,633	394,779
Total assets	2,210,569	1,578,368
Current liabilities:
Accounts payable and accrued liabilities	179,357	110,244
Accounts payable - intercompany	0	0
Asset retirement obligation—current	780	60	60
Short-term derivative instruments	4,808	10,442
Current maturities of long-term debt	156	150
Total current liabilities	185,101	120,896
Long-term derivative instrument	962	0
Asset retirement obligation—long-term	13,988	13,215	13,831
Deferred tax liability	93,957	18,607
Long-term debt, net of current maturities	298,992	298,888
Other non-current liabilities	0	354
Total liabilities	593,000	451,960
Stockholders’ equity:
Common stock	775	674
Paid-in capital	1,399,803	1,036,245
Accumulated other comprehensive loss	(4,841)	(3,429)
Retained earnings (accumulated deficit)	221,832	92,918
Total stockholders’ equity	1,617,569	1,126,408	680,627	632,350
Total liabilities and stockholders’ equity	2,210,569	1,578,368
Parent [Member]
Current assets:
Cash and cash equivalents	93,996	165,293	11,677	93,124
Accounts receivable—oil and gas	47,143	25,070
Accounts receivable-related parties	26,421	33,806
Accounts receivable - intercompany	18,419	15,368
Prepaid expenses and other current assets	4,634	1,506
Deferred tax asset	787
Short-term derivative instruments	1,633	664
Note receivable - related party	875
Total current assets	193,908	241,707
Property and equipment:
Oil and natural gas properties, full-cost accounting	2,247,150	1,606,172
Other property and equipment	10,135	8,642
Accumulated depletion, depreciation, amortization and impairment	(747,677)	(665,864)
Property and equipment, net	1,509,608	948,950
Other assets:
Equity investments	493,860	374,209
Derivative instruments	127
Other assets	12,827	13,295
Total other assets	506,814	387,504
Total assets	2,210,330	1,578,161
Current liabilities:
Accounts payable and accrued liabilities	179,118	110,037
Accounts payable - intercompany	0	0
Asset retirement obligation—current	780	60
Short-term derivative instruments	4,808	10,442
Current maturities of long-term debt	156	150
Total current liabilities	184,862	120,689
Long-term derivative instrument	962
Asset retirement obligation—long-term	13,988	13,215
Deferred tax liability	93,957	18,607
Long-term debt, net of current maturities	298,992	298,888
Other non-current liabilities		354
Total liabilities	592,761	451,753
Stockholders’ equity:
Common stock	775	674
Paid-in capital	1,399,803	1,036,245
Accumulated other comprehensive loss	(4,841)	(3,429)
Retained earnings (accumulated deficit)	221,832	92,918
Total stockholders’ equity	1,617,569	1,126,408
Total liabilities and stockholders’ equity	2,210,330	1,578,161
Guarantor [Member]
Current assets:
Cash and cash equivalents	1,469	1,795	603	772
Accounts receivable—oil and gas	530	545
Accounts receivable-related parties	3,376	1,042
Accounts receivable - intercompany
Prepaid expenses and other current assets		0
Deferred tax asset	0
Short-term derivative instruments		0
Note receivable - related party	0
Total current assets	5,375	3,382
Property and equipment:
Oil and natural gas properties, full-cost accounting	6,455	4,918
Other property and equipment	29	20
Accumulated depletion, depreciation, amortization and impairment	(21)	(20)
Property and equipment, net	6,463	4,918
Other assets:
Equity investments		0
Derivative instruments	0
Other assets		0
Total other assets
Total assets	11,838	8,300
Current liabilities:
Accounts payable and accrued liabilities	239	207
Accounts payable - intercompany	18,309	15,259
Asset retirement obligation—current		0
Short-term derivative instruments		0
Current maturities of long-term debt		0
Total current liabilities	18,548	15,466
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
Other non-current liabilities		0
Total liabilities	18,548	15,466
Stockholders’ equity:
Common stock		0
Paid-in capital	322	322
Accumulated other comprehensive loss		0
Retained earnings (accumulated deficit)	(7,032)	(7,488)
Total stockholders’ equity	(6,710)	(7,166)
Total liabilities and stockholders’ equity	11,838	8,300
Non-Guarantor [Member]
Current assets:
Cash and cash equivalents	1	0	0	1
Accounts receivable—oil and gas	0	0
Accounts receivable-related parties	0	0
Accounts receivable - intercompany	0
Prepaid expenses and other current assets	0	0
Deferred tax asset	0
Short-term derivative instruments	0	0
Note receivable - related party	0
Total current assets	1
Property and equipment:
Oil and natural gas properties, full-cost accounting		0
Other property and equipment		0
Accumulated depletion, depreciation, amortization and impairment		0
Property and equipment, net		0
Other assets:
Equity investments	189,942	172,766
Derivative instruments	0
Other assets		0
Total other assets	189,942	172,766
Total assets	189,943	172,766
Current liabilities:
Accounts payable and accrued liabilities		0
Accounts payable - intercompany	110	109
Asset retirement obligation—current		0
Short-term derivative instruments		0
Current maturities of long-term debt		0
Total current liabilities	110	109
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
Other non-current liabilities		0
Total liabilities	110	109
Stockholders’ equity:
Common stock		0
Paid-in capital	199,437	174,348
Accumulated other comprehensive loss	(3,344)	2,442
Retained earnings (accumulated deficit)	(6,260)	(4,133)
Total stockholders’ equity	189,833	172,657
Total liabilities and stockholders’ equity	189,943	172,766
Eliminations [Member]
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable—oil and gas		0
Accounts receivable-related parties	0	0
Accounts receivable - intercompany	(18,419)	(15,368)
Prepaid expenses and other current assets		0
Deferred tax asset	0
Short-term derivative instruments		0
Note receivable - related party	0
Total current assets	(18,419)	(15,368)
Property and equipment:
Oil and natural gas properties, full-cost accounting		0
Other property and equipment		0
Accumulated depletion, depreciation, amortization and impairment		0
Property and equipment, net		0
Other assets:
Equity investments	(183,123)	(165,491)
Derivative instruments	0
Other assets		0
Total other assets	(183,123)	(165,491)
Total assets	(201,542)	(180,859)
Current liabilities:
Accounts payable and accrued liabilities		0
Accounts payable - intercompany	(18,419)	(15,368)
Asset retirement obligation—current		0
Short-term derivative instruments		0
Current maturities of long-term debt		0
Total current liabilities	(18,419)	(15,368)
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
Other non-current liabilities		0
Total liabilities	(18,419)	(15,368)
Stockholders’ equity:
Common stock		0
Paid-in capital	(199,759)	(174,670)
Accumulated other comprehensive loss	3,344	(2,442)
Retained earnings (accumulated deficit)	13,292	11,621
Total stockholders’ equity	(183,123)	(165,491)
Total liabilities and stockholders’ equity	$ (201,542)	$ (180,859)