Cash, Cash Equivalents, and Investments - Effective Maturity Dates of Available-for-Sale Investments (Detail) $ in Thousands	Jun. 30, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
1 year or less	$ 364,487
1-2 years	293,554
2-3 years	84,104
3-4 years	22,812
4-5 years	2,858
5-7 years	4,704
Fair value	772,519
Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
1 year or less	101,868
1-2 years	103,324
2-3 years	65,231
3-4 years	5,710
4-5 years	2,858
5-7 years	0
Fair value	278,991
Treasury Bills
Debt Securities, Available-for-sale [Line Items]
1 year or less	138,600
1-2 years	158,777
2-3 years	10,113
3-4 years	0
4-5 years	0
5-7 years	0
Fair value	307,490
Asset-Backed Securities
Debt Securities, Available-for-sale [Line Items]
1 year or less	104,998
1-2 years	15,771
2-3 years	8,760
3-4 years	11,199
4-5 years	0
5-7 years	4,704
Fair value	145,432
Sovereign Bonds
Debt Securities, Available-for-sale [Line Items]
1 year or less	5,990
1-2 years	14,833
2-3 years	0
3-4 years	0
4-5 years	0
5-7 years
Fair value	20,823
Agency Bonds
Debt Securities, Available-for-sale [Line Items]
1 year or less	7,783
1-2 years	0
2-3 years	0
3-4 years	5,903
4-5 years	0
5-7 years	0
Fair value	13,686
Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
1 year or less	5,248
1-2 years	849
2-3 years	0
3-4 years	0
4-5 years	0
5-7 years	0
Fair value	$ 6,097