Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Carrying amount of the asset retirement obligations, balance at beginning of period	$ 43,592	$ 41,819
Liabilities settled during the period	(2,321)	(7,835)
Accretion expense	2,659	2,361
Revision of estimated cash flows	(1,825)	7,247
Carrying amount of the asset retirement obligations, balance at end of period	42,105	43,592
Segment Reporting Information [Line Items]
Asset retirement obligations	43,592	$ 41,819	$ 42,105
Other current liabilities
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Carrying amount of the asset retirement obligations, balance at end of period	3,800
Segment Reporting Information [Line Items]
Asset retirement obligations	3,800		3,800
Asset retirement obligation
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Carrying amount of the asset retirement obligations, balance at end of period	38,300
Segment Reporting Information [Line Items]
Asset retirement obligations	$ 38,300		38,300
Bellaire
Segment Reporting Information [Line Items]
Fair value of trust assets			$ 7,900	$ 5,000