Leases (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Capital leased assets
Weighted average remaining lease term	15 years 7 months 6 days
Discount rate	4.20%
Weighted average remaining finance lease term	3 years 7 months 6 days
Finance discount rate	4.00%
Future minimum sublease payments	$ 616,000	$ 1,187,000	$ 1,936,000
Net book value	484,482,000	486,599,000
Lease expenditure	26,968,000	27,734,000	$ 21,956,000
Net book value	$ 23,258,000	14,976,000
Minimum [Member]
Capital leased assets
Finance lease term	1 month
Maximum [Member]
Capital leased assets
Finance lease term	6 years
Computer Equipment [Member]
Capital leased assets
Net book value	$ 12,325,000	10,365,000
Net book value	7,482,000	5,436,000
Yard And Other [Member]
Capital leased assets
Net book value	$ 15,776,000	$ 9,540,000