Goodwill and Other Intangible Assets (Schedule of intangible assets and goodwill) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Amortized intangible assets:
Gross carrying value	$ 66,724	$ 66,724
Accumulated amortization	(15,959)	(11,283)
Net carrying amount	50,765	55,441
Goodwill
Gross carrying value	165,103	166,796
Accumulated amortization
Net carrying amount	165,103	166,796
AEC Trade Names [Member]
Amortized intangible assets:
Gross carrying value	140	140
Accumulated amortization	(128)	(125)
Net carrying amount	$ 12	$ 15
Goodwill
Amortization life in years	15 years	15 years
AEC Technology [Member]
Amortized intangible assets:
Gross carrying value	$ 370	$ 370
Accumulated amortization	(308)	(290)
Net carrying amount	$ 62	$ 80
Goodwill
Amortization life in years	15 years	15 years
Customer Relationships [Member]
Amortized intangible assets:
Gross carrying value	$ 48,421	$ 48,421
Accumulated amortization	(8,076)	(5,654)
Net carrying amount	$ 40,345	$ 42,767
Goodwill
Amortization life in years	15 years	15 years
Customer Contracts [Member]
Amortized intangible assets:
Gross carrying value	$ 17,471	$ 17,471
Accumulated amortization	(7,287)	(5,102)
Net carrying amount	$ 10,184	$ 12,369
Goodwill
Amortization life in years	6 years	6 years
Other Intangible [Member]
Amortized intangible assets:
Gross carrying value	$ 322	$ 322
Accumulated amortization	(160)	(112)
Net carrying amount	$ 162	$ 210
Goodwill
Amortization life in years	5 years	5 years
MC Goodwill [Member]
Goodwill
Gross carrying value	$ 69,373	$ 71,066
Accumulated amortization
Net carrying amount	69,373	71,066
AEC Goodwill [Member]
Goodwill
Gross carrying value	95,730	95,730
Accumulated amortization
Net carrying amount	$ 95,730	$ 95,730