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Fair Value of Financial Assets and Liabilities - Summary of Fair Value and Carrying Value of Long-Term Debt (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total debt $ 1,021,603 $ 1,017,064
Convertible Notes [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value of Convertible Notes 327,000 330,000
Carrying Value of Convertible Notes 316,768 311,544
Senior Secured Notes [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value of Long Term Debt 778,000 782,000
Total debt $ 704,835 $ 705,520