Estimated Useful Lives of Assets (Parenthetical) (Detail) - USD ($) $ in Thousands |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Property, Plant and Equipment [Line Items] | ||
| Accumulated depreciation and amortization | $ 1,500,535 | $ 1,355,218 |
| Property Under Capital Lease | ||
| Property, Plant and Equipment [Line Items] | ||
| Accumulated depreciation and amortization | $ 200,683 | $ 175,166 |
| X | ||||||||||
- Definition Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Details
|