Retirement Benefit Plans (Summary of Net Periodic Benefit Costs) (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
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 0	$ 0	$ 50
Interest cost on benefit obligations			7,941	7,212	7,314
Expected return on plan assets			(11,436)	(12,716)	(12,296)
Recognized net loss			5,705	4,862	5,864
Net periodic benefit cost (benefit)			2,210	(642)	932
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0			0
Interest cost on benefit obligations	65	103	65	103	375
Expected return on plan assets	0	0			0
Recognized net loss	14	2,846			748
Net periodic benefit cost (benefit)	79	2,949			1,123
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0			0
Interest cost on benefit obligations	85	78	$ 85	$ 78	92
Expected return on plan assets	0	0			0
Recognized net loss	(13)	0			0
Net periodic benefit cost (benefit)	$ 72	$ 78			$ 92