Other Asset Impairments Other Asset Impairments (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Asset Impairment Charges [Abstract]
Impairment charges and other	$ (600)	$ 1,300	$ 9,800	$ 0	$ 0	$ 10,480
Texas Sales and Use Tax Assessment Settlement Amount	$ 200					200
Proceeds from sale of aircraft				$ 0	$ 0	$ 12,159