Retirement Benefit Plans - Assets Measured at Fair Value (Details) - Pension Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Recurring [Member] | Cash and cash equivalents [Member]
Assets:
Fair value of plan assets at end of year	$ 17,100	$ 19,400
Fair Value, Recurring [Member] | Government and agency securities [Member]
Assets:
Fair value of plan assets at end of year	38,800	32,600
Fair Value, Recurring [Member] | Corporate bonds [Member]
Assets:
Fair value of plan assets at end of year	79,500	71,700
Fair Value, Recurring [Member] | International Equity Securities [Member]
Assets:
Fair value of plan assets at end of year	100	0
Fair Value, Recurring [Member] | Fixed Income Funds [Member]
Assets:
Fair value of plan assets at end of year	42,000	36,000
Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	66,900	60,800
Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Assets:
Fair value of plan assets at end of year	0	100
Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	36,000	24,000
Net Asset Value [Domain]
Assets:
Fair value of plan assets at end of year	794,900	702,900
Net Asset Value [Domain] | International Equity Securities [Member]
Assets:
Fair value of plan assets at end of year	1,000	2,200
Net Asset Value [Domain] | Common Collective funds - domestic equities [Member]
Assets:
Fair value of plan assets at end of year	76,300	54,000
Net Asset Value [Domain] | Common collective funds - international equities [Member]
Assets:
Fair value of plan assets at end of year	31,900	23,000
Net Asset Value [Domain] | Fixed Income Funds [Member]
Assets:
Fair value of plan assets at end of year	202,500	177,500
Net Asset Value [Domain] | Limited Partnership [Member]
Assets:
Fair value of plan assets at end of year	18,700	24,000
Net Asset Value [Domain] | Real Estate [Member]
Assets:
Fair value of plan assets at end of year	11,200	11,800
Net Asset Value [Domain] | Hedge Funds [Member]
Assets:
Fair value of plan assets at end of year	128,200	122,900
Net Asset Value [Domain] | Defined Benefit Plan, Common Collective Trust [Member]
Assets:
Fair value of plan assets at end of year	17,900	18,500
Net Asset Value [Domain] | Other Assets [Member]
Assets:
Fair value of plan assets at end of year	22,000	20,400
Net Asset Value [Domain] | Cash and Cash Equivalents at Net Asset Value [Member]
Assets:
Fair value of plan assets at end of year	200	200
Level 1 [Member] | Fair Value, Recurring [Member]
Assets:
Fair value of plan assets at end of year	202,500	174,000
Level 1 [Member] | Fair Value, Recurring [Member] | Cash and cash equivalents [Member]
Assets:
Fair value of plan assets at end of year	17,100	19,400
Level 1 [Member] | Fair Value, Recurring [Member] | Government and agency securities [Member]
Assets:
Fair value of plan assets at end of year	35,800	29,900
Level 1 [Member] | Fair Value, Recurring [Member] | Corporate bonds [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | International Equity Securities [Member]
Assets:
Fair value of plan assets at end of year	100	0
Level 1 [Member] | Fair Value, Recurring [Member] | Fixed Income Funds [Member]
Assets:
Fair value of plan assets at end of year	42,000	36,000
Level 1 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	66,900	60,800
Level 1 [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Assets:
Fair value of plan assets at end of year	0	100
Level 1 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	36,000	24,000
Level 2 [Member] | Fair Value, Recurring [Member]
Assets:
Fair value of plan assets at end of year	82,500	74,400
Level 2 [Member] | Fair Value, Recurring [Member] | Cash and cash equivalents [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 2 [Member] | Fair Value, Recurring [Member] | Government and agency securities [Member]
Assets:
Fair value of plan assets at end of year	3,000	2,700
Level 2 [Member] | Fair Value, Recurring [Member] | Corporate bonds [Member]
Assets:
Fair value of plan assets at end of year	79,500	71,700
Level 2 [Member] | Fair Value, Recurring [Member] | International Equity Securities [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 2 [Member] | Fair Value, Recurring [Member] | Fixed Income Funds [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 2 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 2 [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 2 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 3 [Member] | Fair Value, Recurring [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Cash and cash equivalents [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Government and agency securities [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Corporate bonds [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | International Equity Securities [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Fixed Income Funds [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Assets:
Fair value of plan assets at end of year	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	0	0
Assets [Member] | Fair Value, Recurring [Member]
Assets:
Fair value of plan assets at end of year	285,000	248,400
Foreign Plan [Member]
Assets:
Fair value of plan assets at end of year	274,700	254,600
Foreign Plan [Member] | Net Asset Value [Domain]
Assets:
Fair value of plan assets at end of year	231,800	217,800
Equity Option [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	3,200	2,600
Equity Option [Member] | Level 1 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	3,200	2,600
Equity Option [Member] | Level 2 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	0	0
Equity Option [Member] | Level 3 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	0	0
Other Debt Obligations [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	1,400	1,200
Other Debt Obligations [Member] | Level 1 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	1,400	1,200
Other Debt Obligations [Member] | Level 2 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	0	0
Other Debt Obligations [Member] | Level 3 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Assets:
Fair value of plan assets at end of year	$ 0	$ 0