Business Combinations (Details) BTU in Thousands, $ in Thousands	1 Months Ended		12 Months Ended
	Oct. 31, 2017 USD ($)	Aug. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) BTU	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Goodwill			$ 45,732	$ 40,804	$ 30,835
Trade Names [Member]
Business Acquisition [Line Items]
Useful life of intangible assets			15 years
RexCon Inc. [Member]
Business Acquisition [Line Items]
Date of acquisition			Oct. 01, 2017
Cash purchase price	$ 26,443
Amount held in escrow	3,000
Goodwill	3,488
Other intangible assets	$ 7,778
RexCon Inc. [Member] | Maximum [Member]
Business Acquisition [Line Items]
Period of time for amount held in escrow			18 months
RexCon Inc. [Member] | Noncompete agreements [Member]
Business Acquisition [Line Items]
Useful life of intangible assets			5 years
RexCon Inc. [Member] | Technology [Member]
Business Acquisition [Line Items]
Useful life of intangible assets			19 years
RexCon Inc. [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Useful life of intangible assets			15 years
RexCon Inc. [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Useful life of intangible assets			18 years
Power Flame Incorporated [Member]
Business Acquisition [Line Items]
Date of acquisition			Aug. 01, 2016
Cash purchase price		$ 39,765
Amount held in escrow		4,000
Goodwill		12,632
Other intangible assets		$ 17,990
Power Flame Incorporated [Member] | Minimum [Member]
Business Acquisition [Line Items]
Hourly output of gas oil and low NOx burners | BTU			400
Power Flame Incorporated [Member] | Maximum [Member]
Business Acquisition [Line Items]
Period of time for amount held in escrow			2 years
Hourly output of gas oil and low NOx burners | BTU			120,000
Power Flame Incorporated [Member] | Technology [Member]
Business Acquisition [Line Items]
Useful life of intangible assets			19 years
Power Flame Incorporated [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Useful life of intangible assets			15 years
Power Flame Incorporated [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Useful life of intangible assets			18 years