Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) state segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 14, 2014 USD ($)
Revenue Recognition [Abstract]
Revenue recognition period	6 years
Unearned revenue	$ 18,200,000	$ 19,900,000
Noncurrent deferred revenue	$ 4,800,000	7,600,000
Operating Segments [Abstract]
Number of operating segments | segment	1
Number of operating States | state	17
Advertising Costs [Abstract]
Advertising expense	$ 6,500,000	6,600,000	$ 9,800,000
Other Liabilities
Revenue Recognition [Abstract]
Customer deposits	3,300,000	2,100,000
Accrued Liabilities
Other Liabilities [Abstract]
Accrued bonuses	$ 12,700,000	$ 12,600,000
Maine Public Utilities Commission
Revenue Recognition [Abstract]
SQI regulatory examination, recommended penalty				$ 500,000