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Schedule of Effect of Derivative Instruments in Statement of Operations Recognized (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Other (income) expense, net      
Derivative Instruments, Gain (Loss) [Line Items]      
(Gains) losses on derivatives recognized in statements of operations $ (1,133) $ 8,671 $ 3,047