Nonqualified Benefit Plans Components of NPBC (Details 12) - Unfunded Plan - Nonqualified Plan - Supplemental Employee Retirement Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 58	$ 109	$ 185
Interest cost	2,606	3,473	3,157
Recognized net actuarial loss	1,192	764	1,047
Net periodic benefit cost	$ 3,856	$ 4,346	$ 4,389