Fair Value Measurements - Assets Measured at Fair Value on Recurring Basis (Details) - Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Equity Security [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets	$ 11	$ 11
Equity Mutual Fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets	5,907	5,780
U.S. Treasury Mutual Fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets	13,282	13,282
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Security [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets	11	11
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury Mutual Fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets	13,282	13,282
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets	$ 5,907	$ 5,780