Annual report pursuant to Section 13 and 15(d)

Industry Segments Data (Revenue by Customer and Service Type) (Details)

v3.8.0.1
Industry Segments Data (Revenue by Customer and Service Type) (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Revenue from External Customer [Line Items]                      
Revenues $ 235,529 $ 231,214 $ 224,346 $ 228,115 $ 232,293 $ 236,655 $ 233,766 $ 231,098 $ 919,204 $ 933,812 $ 978,534
Wireless                      
Revenue from External Customer [Line Items]                      
Revenues                 272,347 283,156 351,572
Data                      
Revenue from External Customer [Line Items]                      
Revenues                 454,237 436,398 399,685
Video                      
Revenue from External Customer [Line Items]                      
Revenues                 117,648 127,407 133,893
Voice                      
Revenue from External Customer [Line Items]                      
Revenues                 74,972 86,851 93,384
Consumer                      
Revenue from External Customer [Line Items]                      
Revenues                 436,882 452,036 475,259
Consumer | Wireless                      
Revenue from External Customer [Line Items]                      
Revenues                 167,733 177,801 199,862
Consumer | Data                      
Revenue from External Customer [Line Items]                      
Revenues                 145,757 140,196 130,213
Consumer | Video                      
Revenue from External Customer [Line Items]                      
Revenues                 99,609 107,305 115,074
Consumer | Voice                      
Revenue from External Customer [Line Items]                      
Revenues                 23,783 26,734 30,110
Business                      
Revenue from External Customer [Line Items]                      
Revenues                 482,322 481,776 503,275
Business | Wireless                      
Revenue from External Customer [Line Items]                      
Revenues                 104,614 105,355 151,710
Business | Data                      
Revenue from External Customer [Line Items]                      
Revenues                 308,480 296,202 269,472
Business | Video                      
Revenue from External Customer [Line Items]                      
Revenues                 18,039 20,102 18,819
Business | Voice                      
Revenue from External Customer [Line Items]                      
Revenues                 $ 51,189 $ 60,117 $ 63,274