Quarterly report pursuant to Section 13 or 15(d)

Cash, Cash Equivalents, Short-Term and Long-Term Investments - Summary of Cash, Cash Equivalents, Short-Term and Long-Term Investments by Significant Investment Category (Detail)

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Cash, Cash Equivalents, Short-Term and Long-Term Investments - Summary of Cash, Cash Equivalents, Short-Term and Long-Term Investments by Significant Investment Category (Detail) - USD ($)
$ in Thousands
Sep. 30, 2021
Dec. 31, 2020
Sep. 30, 2020
Dec. 31, 2019
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents $ 952,076 $ 1,370,826 $ 1,294,222 $ 824,876
Short-Term Investments 90,577 100,767    
Long-Term Investments 139,052 108,412    
Adjusted Cost 1,181,705 1,580,005    
Fair Value 1,181,705 1,580,005    
Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 195,503 423,865    
Short-Term Investments 7,445 8,067    
Long-Term Investments 16,624 13,079    
Adjusted Cost 219,572 445,011    
Fair Value 219,572 445,011    
Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 83,132 92,700    
Long-Term Investments 122,428 95,333    
Adjusted Cost 205,560 188,033    
Fair Value 205,560 188,033    
Money market funds [Member] | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 195,503 423,865    
Adjusted Cost 195,503 423,865    
Fair Value 195,503 423,865    
U.S. Treasury Securities [Member] | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 7,445 8,067    
Long-Term Investments 16,624 13,079    
Adjusted Cost 24,069 21,146    
Fair Value 24,069 21,146    
Corporate Notes and Bonds [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 81,059 83,521    
Long-Term Investments 52,110 33,732    
Adjusted Cost 133,169 117,253    
Fair Value 133,169 117,253    
Asset-backed Securities [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 2,073 5,498    
Long-Term Investments 18,167 22,755    
Adjusted Cost 20,240 28,253    
Fair Value 20,240 28,253    
Mutual Funds [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 0 0    
Long-Term Investments 52,151 38,846    
Adjusted Cost 52,151 38,846    
Fair Value 52,151 38,846    
U.S. Agency Securities [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments   3,681    
Long-Term Investments   0    
Adjusted Cost   3,681    
Fair Value   3,681    
Cash [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 756,573 946,961    
Fair Value $ 756,573 $ 946,961