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Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Derivative Instruments Liabilities [Member] - Recurring [Member] - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Liabilities [Abstract]      
Total Liabilities $ 4,169 $ 560 $ 18,751
Level 3 [Member]      
Liabilities [Abstract]      
Total Liabilities $ 4,169 $ 560 $ 18,751