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Business Combinations - Business Combinations Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Jan. 05, 2018
Business Acquisition [Line Items]
Percentage of voting interests acquired				100.00%
Silver Spring Networks, Inc. acquisition purchase price, net of cash acquired	$ 802,500
Goodwill		$ 575,750	$ 59,675
SIlver Spring Networks, Inc. [Member]
Business Acquisition [Line Items]
Percentage of voting interests acquired				100.00%
Total net assets acquired				$ 809,216
Cash acquired from acquisition		97,800
Business acquisition, equity interest issued, or issuable, value				$ 6,700
Goodwill		575,800
Acquisition related costs	$ 15,600
Business combination, integration related costs		$ 76,300