Leases (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Weighted average remaining lease term	15 years
Discount rate	4.00%
Weighted average remaining finance lease term	3 years 2 months 12 days
Finance discount rate	3.80%
Future minimum sublease payments	$ 69,000	$ 616,000	$ 1,187,000
Net book value	25,649,000	23,258,000
Net book value	492,127,000	484,482,000
Lease expenditure	$ 26,726,000	26,968,000	$ 27,734,000
Minimum [Member]
Lessee, Lease, Description [Line Items]
Operating leases, remaining life	1 month
Finance leases, remaining life	1 month
Maximum [Member]
Lessee, Lease, Description [Line Items]
Operating leases, remaining life	20 years
Finance leases, remaining life	6 years
Computer Equipment [Member]
Lessee, Lease, Description [Line Items]
Net book value	$ 8,280,000	7,482,000
Net book value	14,254,000	12,325,000
Yard And Others [Member]
Lessee, Lease, Description [Line Items]
Net book value	$ 17,369,000	$ 15,776,000