Leases (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Leases [Line Items]
Right-of-use asset	$ 96,805
Weighted average remaining lease term	14 years 10 months 24 days
Discount rate	4.10%
Weighted average remaining finance lease term	3 years 3 months 18 days
Finance discount rate	3.90%
Future minimum sublease payments	$ 981
Net book value	$ 469,068	$ 486,599
Minimum [Member]
Leases [Line Items]
Operating lease fixed term	1 month
Finance lease term	1 month
Maximum [Member]
Leases [Line Items]
Operating lease fixed term	20 years
Finance lease term	6 years
Computer Equipment [Member]
Leases [Line Items]
Net book value	$ 6,486	5,436
Yard And Other [Member]
Leases [Line Items]
Net book value	8,870
Yard and Auto Equipment [Member]
Leases [Line Items]
Net book value		9,540
Capital Leases [Member]
Leases [Line Items]
Net book value	$ 15,356	$ 14,976	$ 14,976