Business Combinations Pro Forma Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
SIlver Spring Networks, Inc. [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Revenue	$ 585,890	$ 764,654	$ 1,193,111	$ 1,292,509
Business Acquisition, Pro Forma Net Income (Loss)	2,657	20,240	(128,309)	(6,994)
Comverge [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Revenue	585,890	511,024	1,193,111	1,002,786
Business Acquisition, Pro Forma Net Income (Loss)	$ 2,657	$ 18,954	$ (143,009)	$ 34,061