Summary of Significant Accounting Policies - Composition of Underlying Assets Comprising Company's Deferred Compensation Plans Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	$ 462,260	$ 406,634
Quoted Prices in Active Markets for Identical Assets (Level 1)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	462,260	406,634
Significant Other Observable Inputs (Level 2)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	0	0
Significant Unobservable Inputs (Level 3)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	0	0
Money market funds
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	65,681	69,681
Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	65,681	69,681
Money market funds | Significant Other Observable Inputs (Level 2)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	0	0
Money market funds | Significant Unobservable Inputs (Level 3)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	0	0
Mutual funds - bond
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	29,720	27,282
Mutual funds - bond | Quoted Prices in Active Markets for Identical Assets (Level 1)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	29,720	27,282
Mutual funds - bond | Significant Other Observable Inputs (Level 2)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	0	0
Mutual funds - bond | Significant Unobservable Inputs (Level 3)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	0	0
Mutual funds - stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	278,816	234,667
Mutual funds - stock | Quoted Prices in Active Markets for Identical Assets (Level 1)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	278,816	234,667
Mutual funds - stock | Significant Other Observable Inputs (Level 2)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	0	0
Mutual funds - stock | Significant Unobservable Inputs (Level 3)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	0	0
Mutual funds - blend
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	88,043	75,004
Mutual funds - blend | Quoted Prices in Active Markets for Identical Assets (Level 1)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	88,043	75,004
Mutual funds - blend | Significant Other Observable Inputs (Level 2)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	0	0
Mutual funds - blend | Significant Unobservable Inputs (Level 3)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employee deferred compensation trust assets	$ 0	$ 0