Schedule of Unrealized Loss on Available-for-Sale Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	$ 27,556	$ 56,275
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	515	1,616
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	108,781	78,406
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	9,027	9,148
Available-for-sale investments with unrealized losses, Fair Value, Total	136,337	134,681
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	9,542	10,764
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	0	0
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	0	0
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	14,336	16,016
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	2,708	2,889
Available-for-sale investments with unrealized losses, Fair Value, Total	14,336	16,016
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	2,708	2,889
Corporate bonds and direct obligations of government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	20,707	54,031
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	507	1,516
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	92,167	62,390
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	6,251	6,259
Available-for-sale investments with unrealized losses, Fair Value, Total	112,874	116,421
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	6,758	7,775
U.S. Treasury obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	6,849	2,244
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	8	100
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	2,278	0
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	68	0
Available-for-sale investments with unrealized losses, Fair Value, Total	9,127	2,244
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 76	$ 100