Fair Value Measurements - Information about Financial Assets Measured at Fair Value on Recurring Basis Based on Three-Tier Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Level 3 | Investment in Private Equity Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity trading securities	$ 15,000
Level 3 | Redeemable Preferred Stock Investment
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	17,600
Fair Value Measurements Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity securities, debt securities and cash equivalents	863,251	$ 869,684
Fair Value Measurements Recurring | Investment in Private Equity Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity trading securities	15,000
Fair Value Measurements Recurring | Bond Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity trading securities		98,799
Fair Value Measurements Recurring | Exchange Traded Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity trading securities		35,000
Fair Value Measurements Recurring | Redeemable Preferred Stock Investment
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	17,609	21,965
Fair Value Measurements Recurring | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	299,833	332,529
Fair Value Measurements Recurring | U.S. Agency Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	67,493	69,534
Fair Value Measurements Recurring | Municipal Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	24,101	24,480
Fair Value Measurements Recurring | Yankee Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	11,898	12,153
Fair Value Measurements Recurring | Money Market Accounts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents fair value disclosure	105,415	77,067
Fair Value Measurements Recurring | U.S. Government Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	321,902	198,157
Fair Value Measurements Recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity securities, debt securities and cash equivalents	105,415	210,866
Fair Value Measurements Recurring | Level 1 | Bond Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity trading securities		98,799
Fair Value Measurements Recurring | Level 1 | Exchange Traded Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity trading securities		35,000
Fair Value Measurements Recurring | Level 1 | Money Market Accounts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents fair value disclosure	105,415	77,067
Fair Value Measurements Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity securities, debt securities and cash equivalents	725,227	636,853
Fair Value Measurements Recurring | Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	299,833	332,529
Fair Value Measurements Recurring | Level 2 | U.S. Agency Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	67,493	69,534
Fair Value Measurements Recurring | Level 2 | Municipal Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	24,101	24,480
Fair Value Measurements Recurring | Level 2 | Yankee Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	11,898	12,153
Fair Value Measurements Recurring | Level 2 | U.S. Government Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	321,902	198,157
Fair Value Measurements Recurring | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity securities, debt securities and cash equivalents	32,609	21,965
Fair Value Measurements Recurring | Level 3 | Investment in Private Equity Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total equity trading securities	15,000
Fair Value Measurements Recurring | Level 3 | Redeemable Preferred Stock Investment
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total debt securities	$ 17,609	$ 21,965