Fair Value Measurements - Schedule of Company Financial Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fixed Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	$ 9,800
Equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,100
Fair Value, Measurements, Recurring | Mutual Funds Held in Nonqualified SERP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	10,842	$ 13,554
Fair Value, Measurements, Recurring | Fixed Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	9,834
Fair Value, Measurements, Recurring | Equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,061
Fair Value, Measurements, Recurring | Level 1 | Mutual Funds Held in Nonqualified SERP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	10,842	13,554
Fair Value, Measurements, Recurring | Level 1 | Fixed Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	9,834
Fair Value, Measurements, Recurring | Level 1 | Equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,061
Fair Value, Measurements, Recurring | Level 2 | Mutual Funds Held in Nonqualified SERP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0	0
Fair Value, Measurements, Recurring | Level 2 | Fixed Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0
Fair Value, Measurements, Recurring | Level 2 | Equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0
Fair Value, Measurements, Recurring | Level 3 | Mutual Funds Held in Nonqualified SERP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0	$ 0
Fair Value, Measurements, Recurring | Level 3 | Fixed Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0
Fair Value, Measurements, Recurring | Level 3 | Equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	$ 0