Nonqualified Benefit Plans Components of NPBC (Details 2) - Supplemental Employee Retirement Plan - Nonqualified Plan - Unfunded Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 109	$ 185	$ 289
Interest cost	3,473	3,157	3,494
Recognized net actuarial loss	764	1,047	883
Net periodic benefit cost	$ 4,346	$ 4,389	$ 4,666