Benefit Plan Schedule of plan assets and benefit obligation activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Plan Assets, Amount	$ 230,442	$ 210,623	$ 177,077
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	27,800	42,402
Defined Benefit Plan, Plan Assets, Contributions by Employer	0	0
Defined Benefit Plan, Plan Assets, Benefits Paid	7,981	8,856
Defined Benefit Plan, Benefit Obligation	184,410	154,419	123,528
Defined Benefit Plan, Service Cost	8,319	5,873	6,547
Defined Benefit Plan, Interest Cost	5,283	5,491	$ 5,236
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	0	(168)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	24,370	28,551
Benefits paid	7,981	8,856
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 46,032	$ 56,204