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Summary of Significant Accounting Policies - Goodwill, Income Taxes and VIE (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
party
Dec. 31, 2017
USD ($)
Share-Based Compensation    
Number of days prior to the grant that common stock and restricted stock units fair value is determined based on 3 days  
Variable Interest Entity    
Carrying amount asset $ 18,472 $ 18,799
Maximum exposure to loss 18,472 18,799
VIE's assets $ 51,344 $ 41,936
JV building microwave communication networks in US and Asia    
Variable Interest Entity    
Number of other investors in JV | party 9  
Ownership of voting shares of JV held be each investor (as a percent) 11.00%  
Ownership of equity of JV held be each investor (as a percent) 11.00%  
JV building microwave communication networks in US and Europe    
Variable Interest Entity    
Ownership of voting shares (as a percent) 50.00%  
Ownership interest (as a percent) 50.00%