Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies- Commitments as a Result of Acquisitions (Details)

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Commitments and Contingencies- Commitments as a Result of Acquisitions (Details) - EEX
Mar. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Jun. 30, 2014
GBP (£)
Loss Contingencies [Line Items]      
Business combination, contingent consideration arrangements, range of outcomes, value, high (up to) $ 6,304,000   £ 4,500,000
Business combination, contingent consideration, liability $ 0 $ 0