Retirement Benefit Plans (Obligation and Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Amounts recognized in the balance sheets consist of:
Non-current liabilities	$ (10,429)	$ (11,827)
Pension Plan
Change in benefit obligation
Projected benefit obligation at beginning of year	46,065	45,318
Interest cost	1,581	1,746
Actuarial (gain) loss	(3,286)	1,275
Benefits paid	(2,334)	(2,019)
Intercompany transfers	0	255
Projected benefit obligation at end of year	42,026	46,065
Accumulated benefit obligation at end of year	42,026	46,065
Change in plan assets
Fair value of plan assets at beginning of year	38,527	34,628
Actual (loss) return on plan assets	(1,832)	5,461
Employer contributions	593	712
Benefits paid	(2,334)	(2,019)
Intercompany transfers	0	(255)
Fair value of plan assets at end of year	34,954	38,527
Funded status at end of year	(7,072)	(7,538)
Amounts recognized in the balance sheets consist of:
Non-current assets	2,047	2,051
Current liabilities	(588)	(700)
Non-current liabilities	(8,531)	(8,889)
Amount recognized in the balance sheets	(7,072)	(7,538)
Components of accumulated other comprehensive loss (income) consist of:
Actuarial loss	16,277	15,363
Prior service cost	878	937
Deferred taxes	(3,320)	(6,481)
Accumulated other comprehensive (loss) income	13,835	9,819
Other Postretirement Benefits Plan
Change in benefit obligation
Projected benefit obligation at beginning of year	3,221	3,211
Service cost	50	50
Interest cost	98	101
Plan amendments	326	0
Actuarial (gain) loss	(756)	154
Benefits paid	(174)	(295)
Projected benefit obligation at end of year	2,113	3,221
Change in plan assets
Funded status at end of year	(2,113)	(3,221)
Amounts recognized in the balance sheets consist of:
Current liabilities	(215)	(282)
Non-current liabilities	(1,898)	(2,939)
Amount recognized in the balance sheets	(2,113)	(3,221)
Components of accumulated other comprehensive loss (income) consist of:
Actuarial loss	189	1,040
Prior service cost	(339)	(78)
Deferred taxes	(74)	287
Accumulated other comprehensive (loss) income	$ (224)	$ 1,249