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Summary of Significant Accounting Policies - Schedule of financial instruments that are not carried at fair value (Detail) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Assets:    
Carrying Amount, Short-term investments $ 0 $ 21,923
Carrying Amount, Long-term Investments 0 69,699
Assets:    
Fair Value, Short-term investments   21,858
Fair Value, Long-term investments   69,090
2023 Notes [Member]    
Liabilities:    
Notes Payable 750,000 750,000
Liabilities:    
Notes Payable Fair Value Disclosure 766,875 736,725
2027 Notes [Member]    
Liabilities:    
Notes Payable 1,000,000 500,000
Liabilities:    
Notes Payable Fair Value Disclosure $ 1,025,600 $ 482,500