Fair Value of Financial Assets and Liabilities - Summary of Fair Value and Carrying Value of Long-Term Debt (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Mar. 03, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	$ 1,119,713	$ 1,041,948
2024 Senior Secured Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value of Long Term Debt	955,000
Total debt	920,800
2022 Senior Secured Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value of Long Term Debt		737,000
Total debt		702,670
2022 Convertible Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value of Convertible Notes	221,000	216,000
Carrying Value of Convertible Notes	195,867	190,083
2020 Convertible Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value of Convertible Notes	3,000	150,000
Carrying Value of Convertible Notes	$ 3,046	$ 149,195	$ 261,900