Acquisitions Acquisition Detail (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	Oct. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			$ 157	$ 0
Goodwill			$ 19,114	$ 5,789	$ 19,614	$ 5,520
Bolt [Member] [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 32,300	$ 5,200
Goodwill	14,000
Trade Names [Member] | Bolt [Member] [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	$ 7,200
Finite-Lived Intangible Asset, Useful Life	15 years
Customer Relationships [Member] | Bolt [Member] [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	$ 4,200
Finite-Lived Intangible Asset, Useful Life	12 years