Properties and Equipment, Net - Summary of Assets Held-for-sale (Details) - Assets Held-for-sale $ in Thousands	Dec. 31, 2017 USD ($)
ASSETS
Inventories	$ 1,440
Properties and equipment, net	778,855
Assets	780,295
LIABILITIES
Accounts payable	2,352
Asset retirement obligation	15,748
Liabilities	18,100
Net assets	$ 762,195

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