Nonqualified Benefit Plans Investments (Details 16) - Unfunded Plan - Supplemental Employee Retirement Plan - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Investments in nonqualified benefit plans	$ 148,800	$ 134,118
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Investments in nonqualified benefit plans	100,104	87,009
Life insurance carried on plan participants
Defined Benefit Plan Disclosure [Line Items]
Investments in nonqualified benefit plans	39,779	38,659
Other Investments
Defined Benefit Plan Disclosure [Line Items]
Investments in nonqualified benefit plans	$ 8,917	$ 8,450