XML 29 R36.htm IDEA: XBRL DOCUMENT v3.19.3
Fair Value Measurements - Fair Values of Financial Assets Measured on Recurring Basis (Detail) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments $ 443,039 $ 587,964
US treasury notes and bills [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 402,040 467,336
Bond and mutual funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 10,748 10,484
Equity investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 251 234
Term deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments   80,000
Certificate of deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 30,000 29,910
Fair Value, Measurements, Recurring [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total fair value of financial assets 548,861 638,439
Fair Value, Measurements, Recurring [Member] | US treasury notes and bills [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 402,040 517,270
Fair Value, Measurements, Recurring [Member] | Bond and mutual funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 10,748 10,484
Fair Value, Measurements, Recurring [Member] | Equity investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 251 234
Fair Value, Measurements, Recurring [Member] | Money market funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets fair value disclosure 105,822 541
Fair Value, Measurements, Recurring [Member] | Term deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments   80,000
Fair Value, Measurements, Recurring [Member] | Certificate of deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 30,000 29,910
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total fair value of financial assets 343,411 303,576
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | US treasury notes and bills [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 226,590 292,317
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Bond and mutual funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 10,748 10,484
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Equity investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 251 234
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money market funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets fair value disclosure 105,822 541
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Term deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments   0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Certificate of deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total fair value of financial assets 205,450 334,863
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | US treasury notes and bills [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 175,450 224,953
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Bond and mutual funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Equity investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Money market funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets fair value disclosure 0 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Term deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments   80,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Certificate of deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 30,000 29,910
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total fair value of financial assets 0 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | US treasury notes and bills [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Bond and mutual funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Equity investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Money market funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets fair value disclosure 0 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Term deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments   0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Certificate of deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investments $ 0 $ 0