Summary of Significant Accounting Policies (Narrative) (Details)
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12 Months Ended |
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Mar. 09, 2016
USD ($)
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Feb. 19, 2016
USD ($)
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Dec. 31, 2015
USD ($)
well
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Dec. 31, 2014
USD ($)
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Dec. 31, 2013
USD ($)
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Jun. 30, 2017 |
Jun. 30, 2016 |
Apr. 10, 2016
USD ($)
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Dec. 31, 2012
USD ($)
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| Accounting Policies [Line Items] |
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| Proceeds from sale of oil and natural gas properties |
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$ 47,314,000
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$ 5,530,000
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$ 112,201,000
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| Cash and cash equivalents |
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50,074,000
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11,008,000
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32,393,000
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$ 8,901,000
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| Allowance for doubtful accounts |
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$ 0
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0
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507,000
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$ 546,000
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| Discount rate for oil and natural gas prices held constant |
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10.00%
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| Capitalized interest |
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$ 3,900,000
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$ 4,300,000
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$ 3,300,000
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| Expected Forfeitures (percentage) |
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17.50%
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25.50%
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14.00%
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| Amendment No. 8 |
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| Accounting Policies [Line Items] |
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| Revolving credit facility borrowing base |
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$ 200,000,000
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| Maximum | Furniture and equipment |
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| Accounting Policies [Line Items] |
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| Estimated useful lives |
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7 years
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| Minimum | Furniture and equipment |
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| Accounting Policies [Line Items] |
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| Estimated useful lives |
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3 years
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| Scenario Forecast | Amendment No. 8 |
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| Accounting Policies [Line Items] |
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| Leverage ratio |
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2.00
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2.50
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| Interest coverage ratio |
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250.00%
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110.00%
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| Revolving credit facility borrowing base |
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$ 100,000,000
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| Scenario Forecast | Amendment No. 8 | Eurodollar |
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| Accounting Policies [Line Items] |
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| Applicable interest margin (percentage) |
4.00%
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| Scenario Forecast | Amendment No. 8 | Reference Rate |
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| Accounting Policies [Line Items] |
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| Applicable interest margin (percentage) |
3.00%
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| Scenario Forecast | Maximum | Amendment No. 8 |
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| Accounting Policies [Line Items] |
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| Leverage ratio |
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4.0
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| Canada |
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| Accounting Policies [Line Items] |
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| Number of gas wells | well |
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2
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| Subsequent Event | Amendment No. 8 |
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| Accounting Policies [Line Items] |
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| Revolving credit facility borrowing base |
$ 180,000,000
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| Threshold for automatic reductions of the borrowing base in connection with asset sales |
5,000,000
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| Threshold for lenders consent requirement in connection with asset sales |
$ 5,000,000
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| Subsequent Event | Appalchian Basin |
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| Accounting Policies [Line Items] |
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| Proceeds from sale of oil and natural gas properties |
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$ 80,000,000
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