Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Commitments (Details)

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Commitments and Contingencies - Commitments (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jul. 27, 2017
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]          
Rent expense   $ 2.2 $ 1.8 $ 4.4 $ 3.6
Emerging Markets Communications LLC          
Long-term Commitment [Line Items]          
Common stock issued for acquisition (in shares) 5,080,049        
Line of Credit          
Long-term Commitment [Line Items]          
Letters of credit outstanding   7.4   7.4  
Line of Credit | Letters of Credit          
Long-term Commitment [Line Items]          
Letters of credit outstanding   $ 6.2   $ 6.2