Annual report pursuant to Section 13 and 15(d)

Estimated Useful Lives of Assets (Parenthetical) (Detail)

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Estimated Useful Lives of Assets (Parenthetical) (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Property, Plant and Equipment [Line Items]    
Accumulated depreciation and amortization $ 1,571,017 $ 1,500,535
Property Under Capital and Finance Lease    
Property, Plant and Equipment [Line Items]    
Accumulated depreciation and amortization $ 177,733 $ 200,683