Acquisitions - Intangible assets purchase transaction (Details) - USD ($) $ in Thousands		1 Months Ended
	Sep. 30, 2016	Dec. 31, 2017
Zappa Stewart
Identifiable intangible assets purchased
Intangible assets		$ 30,240
Resin Designs
Identifiable intangible assets purchased
Intangible assets	$ 19,450
Customer Relationships | Zappa Stewart
Identifiable intangible assets purchased
Intangible assets		$ 28,500
Useful life		7 years 10 months 24 days
Customer Relationships | Resin Designs
Identifiable intangible assets purchased
Intangible assets	$ 17,500
Useful life	10 years
Technology | Zappa Stewart
Identifiable intangible assets purchased
Intangible assets		$ 900
Useful life		7 years
Technology | Resin Designs
Identifiable intangible assets purchased
Intangible assets	$ 1,200
Useful life	4 years
Trade names | Zappa Stewart
Identifiable intangible assets purchased
Intangible assets		$ 840
Useful life		4 years
Trade names | Resin Designs
Identifiable intangible assets purchased
Intangible assets	$ 750
Useful life	7 years