Investments - Carrying Value and Amortized Cost of Company's Investments Summarized by Major Security Type (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Estimated Fair Value	$ 265,775	$ 250,208
Debt and equity securities, Amortized Cost	266,007	250,182
Debt and equity securities, Unrealized Gains	10	166
Debt and equity securities, Unrealized Losses	(242)	(140)
Debt and equity securities, Estimated Fair Value	265,775	250,208
US Treasury Securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized Cost	112,854	75,315
Debt securities, Unrealized Gains	3	47
Debt securities, Unrealized Losses	(115)	(28)
Debt securities, Estimated Fair Value	112,742	75,334
US Government Sponsored Enterprises Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized Cost	153,153	174,867
Debt securities, Unrealized Gains	7	119
Debt securities, Unrealized Losses	(127)	(112)
Debt securities, Estimated Fair Value	$ 153,033	$ 174,874