Commitments & Contingencies (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) surety_bond	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Commitments [Abstract]
Future minimum operating lease payments due within one year of the balance sheet date	$ 14,200,000
Future minimum operating lease payments due within the second year of the balance sheet date	10,100,000
Future minimum operating lease payments due within the third year of the balance sheet date	4,900,000
Future minimum operating lease payments due within the fourth year of the balance sheet date	2,700,000
Future minimum operating lease payments due within the fifth year of the balance sheet date	2,300,000
Future minimum operating lease payments due within after the fifth year of the balance sheet date	5,800,000
Lease expense	$ 16,500,000	$ 13,000,000	$ 11,100,000
Firm purchase commitment term one	5 years
Firm purchase commitment term two	20 years
Performance Guarantees and Product Warranties [Abstract]
Warranty liability recognized	$ 0
Corporate Guarantees [Abstract]
Letters of credit amount outstanding	36,300,000
Energy Systems Group
Corporate Guarantees [Abstract]
Maximum exposure by parent company on guarantees.	$ 373,000,000
Energy Systems Group | Performance Guarantee
Performance Guarantees and Product Warranties [Abstract]
Number of surety bonds wholly owned subsidiary has outstanding in role as general contractor (in number of surety bonds) | surety_bond	66
Face amount of surety bonds	$ 9,800,000
Work yet to be completed on surety bond projects	29.00%
Period for release of significant portion of surety bonds	P1Y
Energy Systems Group | Performance Guarantee | Maximum
Performance Guarantees and Product Warranties [Abstract]
Face amount of surety bonds	$ 75,900,000