Annual report pursuant to Section 13 and 15(d)

ACQUISITIONS AND DISPOSITIONS Fixed Base Operations ("FBO") (Details)

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ACQUISITIONS AND DISPOSITIONS Fixed Base Operations ("FBO") (Details) - USD ($)
$ in Thousands
12 Months Ended
May 01, 2015
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Proceeds from sale of FBO   $ 0 $ 0 $ 14,252
Gain on sale of FBO   $ 0 $ 0 $ 12,946
Era FBO LLC.        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Percentage of subsidiary acquired 100.00%      
Proceeds from sale of FBO $ 14,300      
Gain on sale of FBO $ 12,900