Retirement Benefit Plans (Changes in Plan Assets and Funded Status of Pension Plans and Other Postretirement Benefit Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in plan assets:
Beginning balance	$ 161,369
Ending balance	192,734	$ 161,369
Pension Plan [Member]
Change in benefit obligation:
Beginning balance	203,645	210,548
Service cost	45	45	$ 40
Interest cost	8,441	8,008	8,068
Actuarial loss (gain)	6,108	(8,588)
Benefit payments, administrative expenses, and interest income, net	(6,731)	(6,368)
Ending balance	211,508	203,645	210,548
Change in plan assets:
Beginning balance	161,369	172,976
Actual return on plan assets	18,284	(5,239)
Employer contributions	20,000	0
Benefits paid and administrative expenses	(6,731)	(6,368)
Ending balance	192,922	161,369	172,976
Funded status of the plan at year end	(18,586)	(42,276)
SERP [Member]
Change in benefit obligation:
Beginning balance	10,518	10,041
Service cost	0	0	0
Interest cost	389	345	364
Actuarial loss (gain)	1,023	373
Benefit payments, administrative expenses, and interest income, net	(124)	(241)
Ending balance	11,806	10,518	10,041
Change in plan assets:
Beginning balance	0	0
Actual return on plan assets	0	0
Employer contributions	124	241
Benefits paid and administrative expenses	(124)	(241)
Ending balance	0	0	0
Funded status of the plan at year end	(11,806)	(10,518)
Other Benefits [Member]
Change in benefit obligation:
Beginning balance	3,853	4,133
Service cost	0	0	0
Interest cost	125	123	139
Actuarial loss (gain)	59	(178)
Benefit payments, administrative expenses, and interest income, net	(185)	(225)
Ending balance	3,852	3,853	4,133
Change in plan assets:
Beginning balance	0	0
Actual return on plan assets	0	0
Employer contributions	185	225
Benefits paid and administrative expenses	(185)	(225)
Ending balance	0	0	$ 0
Funded status of the plan at year end	$ (3,852)	$ (3,853)