Retirement Benefit Plans (Changes in Plan Assets and Funded Status of Pension Plans and Other Postretirement Benefit Plans) (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in plan assets:
Beginning balance	$ 191,972		$ 191,972
Ending balance			239,621	$ 191,972
Funded status of the plan at year end (2)			2,400
Pension Plan [Member]
Change in benefit obligation:
Beginning balance	209,513	$ 229,318	209,513	229,318
Service cost			0	0	$ 50
Interest cost			7,941	7,212	7,314
Actuarial loss (gain)			(33,157)	18,499
Benefits paid and administrative expenses			(9,207)	(8,518)
Ending balance (1)			241,404	209,513	229,318
Change in plan assets:
Beginning balance	191,972	216,225	191,972	216,225
Actual return on plan assets			46,856	(15,735)
Employer contributions			10,000	0
Benefits paid and administrative expenses			(9,207)	(8,518)
Ending balance			239,621	191,972	216,225
Funded status of the plan at year end (2)			(1,783)	(17,541)
SERP [Member]
Change in benefit obligation:
Beginning balance	1,835	13,096	1,835	13,096
Service cost	0	0			0
Interest cost	65	103	65	103	375
Actuarial loss (gain)			(163)	0
Benefits paid and administrative expenses			(128)	(11,364)
Ending balance (1)			1,935	1,835	13,096
Change in plan assets:
Beginning balance	0	0	0	0
Actual return on plan assets			0	0
Employer contributions			128	11,364
Benefits paid and administrative expenses			(128)	(11,364)
Ending balance			0	0	0
Funded status of the plan at year end (2)			(1,935)	(1,835)
Other Benefits [Member]
Change in benefit obligation:
Beginning balance	2,612	3,094	2,612	3,094
Service cost	0	0			0
Interest cost	85	78	85	78	92
Actuarial loss (gain)			103	352
Benefits paid and administrative expenses			(195)	(208)
Ending balance (1)			2,399	2,612	3,094
Change in plan assets:
Beginning balance	$ 0	$ 0	0	0
Actual return on plan assets			0	0
Employer contributions			195	208
Benefits paid and administrative expenses			(195)	(208)
Ending balance			0	0	$ 0
Funded status of the plan at year end (2)			$ (2,399)	$ (2,612)