Cash, Cash Equivalents and Investments - Effective Maturity Dates of Available-for-Sale Investments (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	$ 236,142
1-2 Years	312,021
2-3 Years	112,628
3-4 Years	7,656
4-5 Years	1,147
Fair Value, Total	669,594
Treasury Bills [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	92,914
1-2 Years	187,917
2-3 Years	28,417
3-4 Years	0
4-5 Years	0
Fair Value, Total	309,248
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	65,624
1-2 Years	88,033
2-3 Years	54,208
3-4 Years	4,233
4-5 Years	0
Fair Value, Total	212,098
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	66,680
1-2 Years	17,744
2-3 Years	24,089
3-4 Years	3,423
4-5 Years	1,147
Fair Value, Total	113,083
Sovereign Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	6,294
1-2 Years	16,005
2-3 Years	0
3-4 Years	0
4-5 Years	0
Fair Value, Total	22,299
Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	4,630
1-2 Years	2,322
2-3 Years	0
3-4 Years	0
4-5 Years	0
Fair Value, Total	6,952
Agency Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	0
1-2 Years	0
2-3 Years	5,914
3-4 Years	0
4-5 Years	0
Fair Value, Total	$ 5,914