Subsidiary Guarantor Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net Cash Provided by (Used in) Operating Activities	$ 205,149	$ 139,500
Payments to Explore and Develop Oil and Gas Properties	(196,917)	(129,826)
Payments for Capital Improvements	(1,066)	(821)
Payments to Acquire Businesses, Net of Cash Acquired	(180,825)	6,181
Proceeds from sale of properties and equipment	20	737
Proceeds from divestiture	39,023	0
Purchases of short-term investments	0	(49,890)
Increase (Decrease) in Restricted Cash	1,249	0
intercompany Transfer Investing Activities	0	0
Net Cash Provided by (Used in) Investing Activities	(338,516)	(173,619)
Proceeds from Lines of Credit	35,000
Repayment of revolving credit facility	(35,000)	0
Treasury Stock, Value, Acquired, Cost Method	(2,255)	(2,017)
Other	(379)	(340)
Intercompany Transfers Financing Activities	0	0
Net Cash Provided by (Used in) Financing Activities	(2,634)	(2,357)
Net change in cash, cash equivalents, and restricted cash	(136,001)	(36,476)
Cash, cash equivalents, and restricted cash, beginning of period	189,925	244,100
Cash, cash equivalents, and restricted cash, end of period	53,924	207,624
Corporate, Non-Segment [Member]
Net Cash Provided by (Used in) Operating Activities	149,009	131,661
Payments to Explore and Develop Oil and Gas Properties	(97,286)	(82,489)
Payments for Capital Improvements	(701)	(890)
Payments to Acquire Businesses, Net of Cash Acquired	(180,825)	0
Proceeds from sale of properties and equipment	20	737
Proceeds from divestiture	39,023
Increase (Decrease) in Restricted Cash	1,249
intercompany Transfer Investing Activities	(43,891)	(33,795)
Net Cash Provided by (Used in) Investing Activities	(282,411)	(166,327)
Proceeds from Lines of Credit	35,000
Repayment of revolving credit facility	(35,000)
Treasury Stock, Value, Acquired, Cost Method	(2,255)	(2,017)
Other	(344)	(330)
Intercompany Transfers Financing Activities	0	0
Net Cash Provided by (Used in) Financing Activities	(2,599)	(2,347)
Net change in cash, cash equivalents, and restricted cash	(136,001)	(37,013)
Cash, cash equivalents, and restricted cash, beginning of period	189,925	240,487
Cash, cash equivalents, and restricted cash, end of period	53,924	203,474
Reportable Legal Entities [Member]
Net Cash Provided by (Used in) Operating Activities		7,839
Payments to Explore and Develop Oil and Gas Properties		(47,337)
Payments for Capital Improvements		69
Payments to Acquire Businesses, Net of Cash Acquired		6,181
Proceeds from sale of properties and equipment		0
intercompany Transfer Investing Activities		0
Net Cash Provided by (Used in) Investing Activities		(41,087)
Treasury Stock, Value, Acquired, Cost Method		0
Other		(10)
Intercompany Transfers Financing Activities		33,795
Net Cash Provided by (Used in) Financing Activities		33,785
Net change in cash, cash equivalents, and restricted cash		537
Cash, cash equivalents, and restricted cash, beginning of period		3,613
Cash, cash equivalents, and restricted cash, end of period		4,150
Consolidation, Eliminations [Member]
Net Cash Provided by (Used in) Operating Activities	0	0
Payments to Explore and Develop Oil and Gas Properties	0	0
Payments for Capital Improvements	0	0
Payments to Acquire Businesses, Net of Cash Acquired	0	0
Proceeds from sale of properties and equipment	0	0
Proceeds from divestiture	0
Purchases of short-term investments		0
Increase (Decrease) in Restricted Cash	0
intercompany Transfer Investing Activities	43,891	33,795
Net Cash Provided by (Used in) Investing Activities	43,891	33,795
Proceeds from Lines of Credit	0
Repayment of revolving credit facility	0
Treasury Stock, Value, Acquired, Cost Method	0	0
Other	0	0
Intercompany Transfers Financing Activities	(43,891)	(33,795)
Net Cash Provided by (Used in) Financing Activities	(43,891)	(33,795)
Net change in cash, cash equivalents, and restricted cash	0	0
Cash, cash equivalents, and restricted cash, beginning of period	0	0
Cash, cash equivalents, and restricted cash, end of period	0	0
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Net Cash Provided by (Used in) Operating Activities	56,140
Payments to Explore and Develop Oil and Gas Properties	(99,631)
Payments for Capital Improvements	(365)
Payments to Acquire Businesses, Net of Cash Acquired	0
Proceeds from sale of properties and equipment	0
Proceeds from divestiture	0
Purchases of short-term investments		0
Increase (Decrease) in Restricted Cash	0
intercompany Transfer Investing Activities	0
Net Cash Provided by (Used in) Investing Activities	(99,996)
Proceeds from Lines of Credit	0
Repayment of revolving credit facility	0
Treasury Stock, Value, Acquired, Cost Method	0
Other	(35)
Intercompany Transfers Financing Activities	43,891
Net Cash Provided by (Used in) Financing Activities	43,856
Net change in cash, cash equivalents, and restricted cash	0
Cash, cash equivalents, and restricted cash, beginning of period	0
Cash, cash equivalents, and restricted cash, end of period	$ 0
Parent Company [Member] | Reportable Legal Entities [Member]
Purchases of short-term investments		$ (49,890)