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Acquisitions and Divestitures - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions			3 Months Ended					12 Months Ended
	Dec. 18, 2018	Nov. 01, 2016	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2016
Business Acquisition [Line Items]
Goodwill					$ 211,040			$ 211,040	$ 211,040
Proceeds from sale of assets and equipment								7,089	$ 14,030	$ 3,858
Proceeds from sale of aircraft						$ 4,900	$ 1,300
Gain on sale of asset					300	600	$ 1,300
Proceeds from sale of building					2,400	2,700
Affiliated Entity
Business Acquisition [Line Items]
Proceeds from sale of aircraft					700
Flight Equipment \| Affiliated Entity
Business Acquisition [Line Items]
Gain on sale of asset					$ 700
Blackhawk
Business Acquisition [Line Items]
Goodwill		$ 192,400						192,400
International Services \| Buildings and improvements
Business Acquisition [Line Items]
Proceeds from sale of assets and equipment			$ 2,600	$ 800
Assets Held-for-sale, Not Part of Disposal Group, Other			300
Assets held-for-sale, net book value			$ 5,000			$ 4,100		4,200
Blackhawk
Business Acquisition [Line Items]
Cash payments to acquire business		$ 150,400
Share consideration to acquire business (in shares)		12.8
Total consideration transferred		$ 294,600
Closing share price (USD per share)											$ 11.25
Revenues										10,000
Operating losses										$ (7,400)
Real Property Acquisition From Mosing Companies \| Affiliated Entity
Business Acquisition [Line Items]
Purchase from related party	$ 37,000
Real Property Acquisition From Mosing Companies \| Buildings and improvements \| Affiliated Entity
Business Acquisition [Line Items]
Purchase from related party								$ 18,500