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Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Other assets $ 5,273 $ 4,964
Strategic Investments [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Other assets 3,700 $ 3,500
2022 Notes [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of notes $ 516,400