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
Mar. 31, 2020
Dec. 31, 2019
Mar. 31, 2019
Dec. 31, 2018
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents $ 1,158,766 $ 824,876 $ 687,498 $ 872,237
Short-Term Investments 130,658 112,037    
Long-Term Investments 77,338 94,589    
Adjusted Cost 1,366,762 1,031,502    
Fair Value 1,366,762 1,031,502    
Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 312,117 162,521    
Short-Term Investments 4,771 1,679    
Long-Term Investments 9,179 8,007    
Adjusted Cost 326,067 172,207    
Fair Value 326,067 172,207    
Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 125,887 110,358    
Long-Term Investments 68,159 86,582    
Adjusted Cost 194,046 196,940    
Fair Value 194,046 196,940    
Money market funds [Member] | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 312,117 162,521    
Adjusted Cost 312,117 162,521    
Fair Value 312,117 162,521    
U.S. Treasury Securities | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 4,771 1,679    
Long-Term Investments 9,179 8,007    
Adjusted Cost 13,950 9,686    
Fair Value 13,950 9,686    
Mutual Funds [Member] | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Long-Term Investments 28,102 28,543    
Adjusted Cost 28,102 28,543    
Fair Value 28,102 28,543    
Corporate Notes and Bonds [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 114,583 104,130    
Long-Term Investments 17,319 28,301    
Adjusted Cost 131,902 132,431    
Fair Value 131,902 132,431    
Asset-backed Securities [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 5,262 263    
Long-Term Investments 18,646 23,351    
Adjusted Cost 23,908 23,614    
Fair Value 23,908 23,614    
U.S. Agency Securities | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 6,042 5,965    
Long-Term Investments 4,092 6,387    
Adjusted Cost 10,134 12,352    
Fair Value 10,134 12,352    
Cash [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 846,649 662,355    
Fair Value $ 846,649 $ 662,355