Benefit Plan Schedule of plan assets and benefit obligation activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount	$ 210,623	$ 177,077	$ 195,735
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	42,402	(8,118)
Defined Benefit Plan, Plan Assets, Contributions by Employer	0	0
Defined Benefit Plan, Plan Assets, Benefits Paid	8,856	10,540
Defined Benefit Plan, Benefit Obligation	154,419	123,528	138,698
Defined Benefit Plan, Service Cost	5,873	6,547	5,270
Defined Benefit Plan, Interest Cost	5,491	5,236	$ 5,085
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	(168)	0
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	28,551	(16,413)
Benefits paid	8,856	10,540
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 56,204	$ 53,549