Fair Value Measurements - Schedule of Fair Value Information for Financial Assets and Liabilities Carried on Balance Sheet (Parenthetical) (Detail)	Jun. 30, 2020	Dec. 31, 2019
4.25% Convertible Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	4.25%
3.90% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	3.90%
4% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	4.00%
4.55% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	4.55%
Estimate of Fair Value Measurement [Member] | 4.25% Convertible Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	4.25%	4.25%
Estimate of Fair Value Measurement [Member] | 3.90% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	3.90%
Estimate of Fair Value Measurement [Member] | 4% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	4.00%	4.00%
Estimate of Fair Value Measurement [Member] | 3.75% Callable Promissory Note
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	3.75%	3.75%
Estimate of Fair Value Measurement [Member] | 4.55% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	4.55%	4.55%
Estimate of Fair Value Measurement [Member] | 3.95% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate		3.95%
Carrying Value [Member] | 4.25% Convertible Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	4.25%	4.25%
Carrying Value [Member] | 3.90% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	3.90%
Carrying Value [Member] | 4% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	4.00%	4.00%
Carrying Value [Member] | 3.75% Callable Promissory Note
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	3.75%	3.75%
Carrying Value [Member] | 4.55% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	4.55%	4.55%
Carrying Value [Member] | 3.95% Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate		3.95%