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Fair Value Measurement - Summary of Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost $ 325,163 $ 368,753
Gross Unrealized Gains 48 51
Gross Unrealized Losses (26,648) (28,802)
Recorded Basis 298,563 340,002
Cash and Cash Equivalents [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 26,661 19,539
Recorded Basis 26,661 19,539
Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 72,886 88,496
Gross Unrealized Gains 15 6
Gross Unrealized Losses (6,409) (7,475)
Recorded Basis 66,492 81,027
Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 225,616 260,718
Gross Unrealized Gains 33 45
Gross Unrealized Losses (20,239) (21,327)
Recorded Basis 205,410 239,436
Money Market Funds [Member] | Cash and Cash Equivalents [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 26,661 19,539
Recorded Basis 26,661 19,539
Money Market Funds [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 216 337
Recorded Basis 216 337
Corporate Bonds [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 27,954 34,472
Gross Unrealized Gains 3 2
Gross Unrealized Losses (2,365) (3,161)
Recorded Basis 25,592 31,313
Corporate Bonds [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 100,030 82,481
Gross Unrealized Gains 16 19
Gross Unrealized Losses (7,302) (8,473)
Recorded Basis 92,744 74,027
U.S. Government Agency Securities [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 12,734 12,830
Gross Unrealized Losses (203) (408)
Recorded Basis 12,531 12,422
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 16,785 16,863
Gross Unrealized Losses (914) (1,199)
Recorded Basis 15,871 15,664
U.S. Treasuries [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 12,460 12,448
Gross Unrealized Losses (1,140) (1,253)
Recorded Basis 11,320 11,195
U.S. Treasuries [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 54,900 109,020
Gross Unrealized Gains   21
Gross Unrealized Losses (6,348) (6,436)
Recorded Basis 48,552 102,605
Mortgage-Backed Securities [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 12,128 13,084
Gross Unrealized Losses (2,592) (2,454)
Recorded Basis 9,536 10,630
Mortgage-Backed Securities [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 40,858 42,077
Gross Unrealized Gains 10 2
Gross Unrealized Losses (5,674) (5,218)
Recorded Basis 35,194 36,861
Asset-Backed Securities [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 7,610 13,659
Gross Unrealized Gains 12 4
Gross Unrealized Losses (109) (191)
Recorded Basis 7,513 13,472
Asset-Backed Securities [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 1,666 799
Gross Unrealized Gains 6 1
Gross Unrealized Losses (1) (1)
Recorded Basis 1,671 799
Emerging Markets [Member] | Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost   2,003
Gross Unrealized Losses   (8)
Recorded Basis   1,995
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 1 2
Recorded Basis 201 202
Mutual Funds [Member] | Restricted Cash and Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cost 10,961 8,941
Recorded Basis $ 10,961 $ 8,941