Income Taxes Schedule of Deferred Tax Liabilities (Details) $ in Thousands	Sep. 30, 2018 USD ($)
Income Tax Disclosure [Abstract]
Oil and natural gas properties	$ (322,911)
Derivative contracts	22,530
Other	719
Deferred tax liabilities, net	$ 299,662

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from derivative instruments.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences, classified as other.

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