Summary of Significant Accounting Policies - EPS and New Accounting Pronouncements (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) item shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares
Denominator used to compute basic and diluted earnings per share
Basic earnings per share - weighted average shares	11,503,296	10,977,341	10,591,351
Effect of dilutive securities:
Employee and director restricted stock units (in shares)	52,701	83,727	143,787
Warrants (in shares)		325,235	572,913
Diluted earnings per share - weighted average shares	11,555,997	11,386,303	11,308,051
Advertising
Advertising expense | $	$ 6.1	$ 5.9	$ 6.1
Buildings | Minimum
Effect of dilutive securities:
Average economic lives	18 years
Buildings | Maximum
Effect of dilutive securities:
Average economic lives	34 years
Cable and wire | Minimum
Effect of dilutive securities:
Average economic lives	11 years
Cable and wire | Maximum
Effect of dilutive securities:
Average economic lives	37 years
Switching and circuit equipment | Minimum
Effect of dilutive securities:
Average economic lives	6 years
Switching and circuit equipment | Maximum
Effect of dilutive securities:
Average economic lives	15 years
Other property | Minimum
Effect of dilutive securities:
Average economic lives	4 years
Other property | Maximum
Effect of dilutive securities:
Average economic lives	17 years
Software
Effect of dilutive securities:
Average economic lives	5 years
Number of stages for segregation of project costs associated with internally developed software | item	3