(Intangible Assets Acquired from Business Acquisitions) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 1,700	$ 1,800
Intangible assets
Gross Carrying Amount	84,658		$ 84,658
Accumulated Amortization	(43,879)		(42,132)
Net Carrying Value	40,779		42,526
TES [Member]
Intangible assets
Gross Carrying Amount	55,008		55,008
Accumulated Amortization	(24,051)		(22,959)
Net Carrying Value	30,957		32,049
LTL
Intangible assets
Gross Carrying Amount	2,498		2,498
Accumulated Amortization	(1,967)		(1,925)
Net Carrying Value	531		573
Ascent [Member]
Intangible assets
Gross Carrying Amount	27,152		27,152
Accumulated Amortization	(17,861)		(17,248)
Net Carrying Value	$ 9,291		$ 9,904