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)

v3.10.0.1
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, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents $ 872,237 $ 736,431 $ 718,536 $ 507,991
Short-Term Investments 100,029      
Long-Term Investments 93,745 17,396    
Adjusted Cost 1,066,011 753,827    
Fair Value 1,066,011 753,827    
Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 158,613      
Short-Term Investments 4,979      
Long-Term Investments 1,976      
Adjusted Cost 165,568      
Fair Value 165,568      
Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 95,050      
Long-Term Investments 91,769      
Adjusted Cost 186,819      
Fair Value 186,819      
Money market funds [Member] | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 158,613      
Adjusted Cost 158,613      
Fair Value 158,613      
U.S. Treasury Securities | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 4,979      
Long-Term Investments 1,976      
Adjusted Cost 6,955      
Fair Value 6,955      
Mutual Funds [Member] | Level 1 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Long-Term Investments 20,957 17,396    
Adjusted Cost 20,957 17,396    
Fair Value 20,957 17,396    
Corporate Notes and Bonds [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 88,412      
Long-Term Investments 43,868      
Adjusted Cost 132,280      
Fair Value 132,280      
Asset-backed Securities [Member] | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 2,115      
Long-Term Investments 21,195      
Adjusted Cost 23,310      
Fair Value 23,310      
U.S. Agency Securities | Level 2 [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Short-Term Investments 4,523      
Long-Term Investments 5,749      
Adjusted Cost 10,272      
Fair Value 10,272      
Cash [Member]        
Cash Cash Equivalents Short Term And Long Term Investments [Line Items]        
Cash and cash equivalents 713,624 736,431    
Fair Value $ 713,624 $ 736,431