Pension Plans (Pension Plan Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned during the year	$ 5,234	$ 5,100	$ 4,897
Interest cost on projected benefit obligation	(21,020)	(26,422)	(23,804)
Expected return on plan assets	(43,183)	(42,560)	(47,841)
Recognized net loss	4,804	15,260	11,370
Additional amount recognized due to curtailment/settlement	0	0	0
Net pension benefit cost (income)	(12,125)	4,222	(7,770)
Change in net gain or (loss)	(708)	3,295	27,203
Amortization of net loss	(4,804)	(15,260)	(11,370)
Total recognized in other comprehensive (loss) income	(5,512)	(11,965)	15,833
Total recognized in net periodic benefit cost and other comprehensive (loss) income	(17,637)	(7,743)	8,063
SERP
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned during the year	0	0	0
Interest cost on projected benefit obligation	(165)	(237)	(246)
Expected return on plan assets	0	0	0
Recognized net loss	944	245	248
Additional amount recognized due to curtailment/settlement	0	0	46
Net pension benefit cost (income)	1,109	482	540
Change in net gain or (loss)	703	720	(325)
Amortization of net loss	(944)	(245)	(248)
Total recognized in other comprehensive (loss) income	(241)	475	(573)
Total recognized in net periodic benefit cost and other comprehensive (loss) income	$ 868	$ 957	$ (33)