Annual report pursuant to Section 13 and 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
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents $ 1,370,826 $ 824,876 $ 872,237 $ 736,431
Short-Term Investments 100,767 112,037    
Long-Term Investments 108,412 94,589    
Adjusted Cost 1,580,005 1,031,502    
Fair Value 1,580,005 1,031,502    
Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 423,865 162,521    
Short-Term Investments 8,067 1,679    
Long-Term Investments 13,079 8,007    
Adjusted Cost 445,011 172,207    
Fair Value 445,011 172,207    
Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 92,700 110,358    
Long-Term Investments 95,333 86,582    
Adjusted Cost 188,033 196,940    
Fair Value 188,033 196,940    
Money market funds [Member] | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 423,865 162,521    
Adjusted Cost 423,865 162,521    
Fair Value 423,865 162,521    
U.S. Treasury Securities [Member] | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 8,067 1,679    
Long-Term Investments 13,079 8,007    
Adjusted Cost 21,146 9,686    
Fair Value 21,146 9,686    
Mutual Funds [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Long-Term Investments 38,846 28,543    
Adjusted Cost 38,846 28,543    
Fair Value 38,846 28,543    
Corporate Notes and Bonds [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 83,521 104,130    
Long-Term Investments 33,732 28,301    
Adjusted Cost 117,253 132,431    
Fair Value 117,253 132,431    
Asset-backed Securities [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 5,498 263    
Long-Term Investments 22,755 23,351    
Adjusted Cost 28,253 23,614    
Fair Value 28,253 23,614    
U.S. Agency Securities [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 3,681 5,965    
Long-Term Investments   6,387    
Adjusted Cost 3,681 12,352    
Fair Value 3,681 12,352    
Cash [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 946,961 662,355    
Fair Value $ 946,961 $ 662,355