LONG-TERM DEBT (Details Textual) - USD ($)		1 Months Ended			3 Months Ended					6 Months Ended		9 Months Ended		12 Months Ended
	Feb. 10, 2014	Apr. 18, 2017	Apr. 21, 2016	Apr. 17, 2015	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount					$ 817,000							$ 817,000
Debt Instrument, Description		The 2017 Credit Facility matures on the earlier of (i) April 18, 2023, or (ii) in the event such debt is not repaid or refinanced, 91 days prior to the maturity of either of the Company's 2022 Notes or the Company's 2020 Notes. At the Company's election, the interest rate on borrowings under the 2017 Credit Facility are based on either (i) the then applicable base rate (as defined in the 2017 Credit Facility) as, for any day, a rate per annum (rounded upward, if necessary, to the next 1/100th of 1%) equal to the greater of (a) the prime rate published in the Wall Street Journal, (b) 1/2 of 1% in excess rate of the overnight Federal Funds Rate at any given time, (c) the one-month LIBOR rate commencing on such day plus 1.00%) and (d) 2%, or (ii) the then applicable LIBOR rate (as defined in the 2017 Credit Facility). The average interest rate was approximately 5.91% for 2018 and was 5.31% for 2017.										The 2022 Notes were offered at an original issue price of 100.0% plus accrued interest from April 17, 2015, and will mature on April 15, 2022. Interest on the 2022
Gains (Losses) on Extinguishment of Debt, Total					120,000		$ 1,200,000		$ 690,000			$ 985,000	$ (6,393,000)	$ 7,100,000
Debt Instrument, Interest Rate Terms		The 2017 Credit Facility contains customary representations and warranties and events of default, affirmative and negative covenants (in each case, subject to materiality exceptions and qualifications) which may be more restrictive than those governing the Notes. The 2017 Credit Facility also contains certain financial covenants, including a maintenance covenant requiring the Company's interest expense coverage ratio (defined as the ratio of consolidated EBITDA to consolidated interest expense) to be greater than or equal to 1.25 to 1.00 and its total senior secured leverage ratio (defined as the ratio of consolidated net senior secured indebtedness to consolidated EBITDA) to be less than or equal to 5.85 to 1.00.										At the Company’s election, the interest rate on borrowings under the 2017 Credit Facility are based on either (i) the then applicable base rate (as defined in the 2017 Credit Facility) as, for any day, a rate per annum (rounded upward, if necessary, to the next 1/100th of 1%) equal to the greater of (a) the prime rate published in the Wall Street Journal, (b) 1/2 of 1% in excess rate of the overnight Federal Funds Rate at any given time, (c) the one-month LIBOR rate commencing on such day plus 1.00%) and (d) 2%, or (ii) the then applicable LIBOR rate (as defined in the 2017 Credit Facility). The average interest rate was approximately 5.91% for 2018 and was 5.31% for 2017.
Interest Expense, Total					18,987,000				19,938,000			$ 57,423,000	60,147,000
Debt Instrument Additional Interest Payment Term On Prepayment		Beginning with the interest payment date occurring in June 2017 and ending in March 2023, the Company will be required to repay principal, to the extent then outstanding, equal to 1/4 of 1% of the aggregate initial principal amount of all term loans incurred on the effective date of the 2017 Credit Facility.
Payments Under 2017 Credit Facility					2,600,000				1,800,000			2,600,000	1,800,000
Comcast Note [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount					11,900,000		11,900,000	$ 11,900,000				11,900,000		11,900,000
Long-term Debt, Gross					$ 11,900,000							$ 11,900,000
Debt Instrument, Interest Rate, Stated Percentage					10.47%							10.47%
Debt Financing Cost [Member]
Debt Instrument [Line Items]
Interest Expense, Total					$ 718,000				718,000			$ 2,200,000	2,900,000
2022 Notes
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 350,000,000
Debt Instrument, Interest Rate, Stated Percentage				7.375%
Debt Instrument, Description				an original issue price of 100.0% plus accrued interest
9.25% Senior Subordinated Notes due February 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					$ 245,000,000		275,000,000	275,000,000				$ 245,000,000		275,000,000
Debt Instrument, Interest Rate, Stated Percentage					9.25%							9.25%
Gains (Losses) on Extinguishment of Debt, Total						$ 239,000				$ 626,000		$ 120,000	690,000
9.25% Senior Subordinated Notes due February 2020 [Member] | Private Offering [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 335,000,000
Debt Instrument, Interest Rate, Stated Percentage	9.25%
Debt Instrument, Periodic Payment	$ 15,500,000
2015 Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 350,000,000
Debt Instrument, Description												(i) the then applicable base rate plus 3.5% (as defined in the 2015 Credit Facility) as, for any day, a rate per annum (rounded upward, if necessary, to the next 1/100th of 1%) equal to the greater of (a) the prime rate published in the Wall Street Journal, (b) a rate of 1/2 of 1% in excess rate of the overnight Federal Funds Rate at any given time, and (c) the one-month LIBOR commencing on such day plus 1.00%), or (ii) the then applicable LIBOR rate plus 4.5% (as defined in the 2015 Credit Facility). The average interest rate was approximately 5.32% for 2017 and 5.13% for 2016.
Asset Backed Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 25,000,000
Percentage Borrowing Of Eligible Accounts			(85.00%)
Credit Facility 2017 [Member]
Debt Instrument [Line Items]
Covenant Compliance Description For Maintaining Interest Coverage Ratio												maintaining an interest coverage ratio of no less than:1.25 to 1.00 on June 30, 2017 and the last day of each fiscal quarter thereafter.
Covenant Compliance Description For Maintaining Total Leverage Ratio												maintaining a senior leverage ratio of no greater than: 5.85 to 1.00 on June 30, 2017 and the last day of each fiscal quarter thereafter.
Repayments of Long-term Debt, Total					$ 875,000				875,000		$ 875,000	$ 875,000	875,000
Long-term Debt, Gross					344,800,000		347,400,000	347,400,000				344,800,000		347,400,000
Senior Subordinated Notes Due From 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Periodic Payment, Interest	$ 11,600,000
Gains (Losses) on Extinguishment of Debt, Total							1,200,000
Debt Instrument, Repurchase Amount					$ 5,000,000	$ 11,000,000	$ 20,000,000	$ 20,000,000	$ 20,000,000	$ 14,000,000		$ 5,000,000	$ 20,000,000	$ 20,000,000
Debt Instrument, Redemption Price, Percentage							97.375%	93.625%	96.00%	95.125%		97.25%