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Fair Value Measurement - Summary of Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Mar. 31, 2025
Dec. 31, 2024
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost $ 334,317 $ 325,163
Gross Unrealized Gains 111 48
Gross Unrealized Losses (22,437) (26,648)
Recorded Basis 311,991 298,563
Cash and Cash Equivalents [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 8,660 26,661
Recorded Basis 8,660 26,661
Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 72,614 72,886
Gross Unrealized Gains 4 15
Gross Unrealized Losses (5,458) (6,409)
Recorded Basis 67,160 66,492
Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 253,043 225,616
Gross Unrealized Gains 107 33
Gross Unrealized Losses (16,979) (20,239)
Recorded Basis 236,171 205,410
Money Market Funds [Member] | Cash and Cash Equivalents [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 8,660 26,661
Recorded Basis 8,660 26,661
Money Market Funds [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 424 216
Recorded Basis 424 216
Corporate Bonds [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 27,928 27,954
Gross Unrealized Gains 4 3
Gross Unrealized Losses (1,950) (2,365)
Recorded Basis 25,982 25,592
Corporate Bonds [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 96,896 100,030
Gross Unrealized Gains 33 16
Gross Unrealized Losses (6,079) (7,302)
Recorded Basis 90,850 92,744
U.S. Government Agency Securities [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 12,710 12,734
Gross Unrealized Losses (121) (203)
Recorded Basis 12,589 12,531
U.S. Government Agency Securities [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 16,775 16,785
Gross Unrealized Losses (738) (914)
Recorded Basis 16,037 15,871
U.S. Treasuries [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 12,462 12,460
Gross Unrealized Losses (911) (1,140)
Recorded Basis 11,551 11,320
U.S. Treasuries [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 86,116 54,900
Gross Unrealized Gains 8  
Gross Unrealized Losses (5,236) (6,348)
Recorded Basis 80,888 48,552
Mortgage-Backed Securities [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 11,917 12,128
Gross Unrealized Losses (2,366) (2,592)
Recorded Basis 9,551 9,536
Mortgage-Backed Securities [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 39,853 40,858
Gross Unrealized Gains 52 10
Gross Unrealized Losses (4,926) (5,674)
Recorded Basis 34,979 35,194
Asset-Backed Securities [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 7,597 7,610
Gross Unrealized Gains   12
Gross Unrealized Losses (110) (109)
Recorded Basis 7,487 7,513
Asset-Backed Securities [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 1,713 1,666
Gross Unrealized Gains 10 6
Gross Unrealized Losses   (1)
Recorded Basis 1,723 1,671
Emerging Markets [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 200 200
Gross Unrealized Gains 4 1
Recorded Basis 204 201
Mutual Funds [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 11,066 10,961
Recorded Basis $ 11,066 $ 10,961