Fair Value Measurement - Summary of Fair Value Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Derivative asset - embedded conversion feature	$ 73,298	$ 80,651	[1]
Fair Value Measurements Recurring [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Derivative asset - embedded conversion feature	73,298	80,651
Fair Value Measurements Recurring [Member] | Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Derivative asset - embedded conversion feature	$ 73,298	$ 80,651

[1] Balances derived from audited financial statements as of December 31, 2016.