Summary of Significant Accounting Policies - Company's Income from Investments Held in Employee Deferred Compensation Trusts (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accounting Policies [Abstract]
Dividend income	$ 443	$ 732	$ 1,887	$ 3,594
Realized and unrealized gain	25,652	718	32,743	31,034
Deferred Compensation Plan, Investment Income	$ 26,095	$ 1,450	$ 34,630	$ 34,628