Pension Plans (Pension Plan Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned during the year	$ 4,794	$ 4,596	$ 14,131
Interest cost on projected benefit obligation	(24,358)	(24,488)	(27,514)
Expected return on plan assets	(42,049)	(40,767)	(44,130)
Amortization of prior service cost	0	0	57
Recognized net loss	13,943	12,694	9,920
Additional amount recognized due to curtailment/settlement	0	0	0
Net pension benefit cost	1,046	1,011	7,492
Change in net gain or (loss)	(6,607)	19,126	29,923
Amortization of prior service cost	0	0	(57)
Amortization of net loss	(13,943)	(12,694)	(9,920)
Total recognized in other comprehensive income (loss)	(20,550)	6,432	19,946
Total recognized in net periodic benefit cost and other comprehensive income (loss)	(19,504)	7,443	27,438
SERP
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned during the year	0	0	206
Interest cost on projected benefit obligation	(241)	(254)	(318)
Expected return on plan assets	0	0	0
Amortization of prior service cost	0	0	0
Recognized net loss	146	182	218
Additional amount recognized due to curtailment/settlement	305	0	0
Net pension benefit cost	692	436	742
Change in net gain or (loss)	347	155	(155)
Amortization of prior service cost	0	0	0
Amortization of net loss	(146)	(182)	(218)
Total recognized in other comprehensive income (loss)	201	(27)	(373)
Total recognized in net periodic benefit cost and other comprehensive income (loss)	$ 893	$ 409	$ 369