Nature of Business and Significant Accounting Policies - Allowance From Doubtful Accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts receivable:
Threshold period for considering receivable as past due	90 days
Changes in the allowance for doubtful accounts
Beginning of Year	$ 1,711,000	$ 1,512,000	$ 1,073,000
Additions	756,000	398,000	920,000
Write-offs	160,000	201,000	482,000
Recoveries	20,000	1,000	1,000
End of Year	2,327,000	1,711,000	1,512,000
Programming rights:
Impairment of programming rights	0	0	0
Amortization of programming rights	11,806,000	12,182,000	$ 11,703,000
Accumulated amortization of programming rights	$ 32,600,000	$ 20,800,000