Organization and Summary of Significant Accounting Policies - Other Assets (Details) - USD ($) $ in Thousands	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deposit for surety bonds		$ 8,300	$ 0
Gulf of Mexico Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deposit for surety bonds		$ 8,300
Subsequent Event | Gulf of Mexico Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase commitment	$ 3,800
Other Noncurrent Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deposit for surety bonds			$ 6,200