Income Taxes Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 0
Increase resulting from tax positions acquired	7,111
Increase resulting from prior period tax positions	4
Increase resulting from current period tax positions	0
Balance at end of year	7,115
Less: Effects of temporary items	(4,666)
Total that, if recognized, would impact the effective income tax rate as of the end of the year	2,449	$ 0	$ 0
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	395,100
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration	172,700
Deferred Tax Assets, Valuation Allowance	(13,900)
Operating Loss Carryforwards	$ 8,300
Minimum [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2032
Maximum [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037
Energen [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Deferred Tax Assets, Valuation Allowance	$ (13,600)