Summary of Significant Accounting Policies - Company's Income from Investments Held in Employee Deferred Compensation Trusts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Dividend income	$ (8,322)	$ (10,425)	$ (10,857)
Realized and unrealized (gains) losses	(66,866)	(44,492)	22,343
Deferred Compensation Plan, Investment Income	$ (75,188)	$ (54,917)	$ 11,486