Annual report pursuant to Section 13 and 15(d)

Variable Interest Entities (Equity Method Investment) (Details)

v3.8.0.1
Variable Interest Entities (Equity Method Investment) (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Jun. 30, 2015
Schedule of Equity Method Investments [Line Items]        
Impairment of equity method investment $ 0 $ 0 $ 12,593,000  
Exposure to loss related with VIE $ 0      
Next Generation Carrier-Class Communications Services Firm        
Schedule of Equity Method Investments [Line Items]        
Ownership percentage       40.80%
Fair value of equity investment       $ 0