Condensed Consolidated Balance Sheets Parenthetical - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Other property and equipment, accumulated depreciation	$ 56,067	$ 49,985
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	200,000,000	200,000,000
Common Stock, Shares, Issued	112,137,582	111,687,016
Common Stock, Shares, Outstanding	112,137,582	111,687,016