Decommissioning and Other Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Decommissioning and Other Asset Retirement Obligations Detail [Table]
Beginning balance for the period, as reported	$ 55,478	$ 57,449
Activity in the period:
Accretion of liability	2,051	2,249
Retirement obligations incurred	265	0
Revisions in estimated cash flows		(180)
Settlement of retirement obligations	(572)	(4,040)
Ending balance at December 31	58,402	55,478	$ 57,449
Change in estimated cash flows to decommission oil and gas properties	1,180
Direct charges to operating expense for increased estimated cash flows	0	2,629	$ 2,661
Estimated future hurricane repair expenses	8,200
Asset retirement obligations associated with non-operated properties	$ 11,700	$ 9,400