Supplemental Cash Flow Information - Summary of Supplemental Cash Flow Information (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Cash paid for interest	$ 122,940	$ 138,346
Cash paid for income taxes	0	2
Cash received for income tax refunds	5	148
Noncash Investing and Financing Items [Abstract]
Accrued capital expenditures	317,500		$ 302,800
Increase (Decrease) in Asset Retirement Obligations	$ 3,562	$ 3,771

Future cash outflow to pay for purchases of fixed assets that have occurred.

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income.

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The increase (decrease) during the reporting period in the carrying amount of asset retirement obligations.

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Amount of cash paid for interest, including, but not limited to, capitalized interest and payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount; classified as operating and investing activities.

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The amount of cash received during the period as refunds for the overpayment of taxes.

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