DEBT - 2018 Credit Facility (Details)				3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 01, 2019	May 16, 2018 USD ($)	May 08, 2018 USD ($)	Sep. 30, 2018 USD ($) agreement	Sep. 30, 2018 USD ($) agreement	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Proceeds from revolver						$ 25,000,000	$ 10,000,000	$ 0
Principal payments of convertible senior notes						126,892,000	0	0
Repayments of senior debt						146,625,000	3,375,000	$ 0
Total						$ 6,644,000	$ 14,750,000
Credit Facility 2018
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 340,000,000
New debt issuance costs			7,482,000
Previously incurred unamortized debt issuance costs or discount			3,919,000
Total			11,401,000
$215 million First Lien Term Loan
Line of Credit Facility [Line Items]
Maximum borrowing capacity			215,000,000
Proceeds from revolver			215,000,000
Debt instrument, periodic payment					$ 500,000
Repayments of senior debt				$ 15,000,000
$75 million Second Lien Term Loan
Line of Credit Facility [Line Items]
Maximum borrowing capacity			75,000,000
Proceeds from revolver			75,000,000
$50 million Revolver
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 50,000,000
Convertible Senior Notes | Convertible Notes
Line of Credit Facility [Line Items]
Principal payments of convertible senior notes		$ 126,900,000
Eurodollar Rate | First Lien Term Loan Facility And Revolving Loan Facility 2018, Eurodollar Loans
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			4.50%
Eurodollar Rate | First Lien Term Loan Facility And Revolving Loan Facility 2018, Base Rate Loans
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			1.00%
Basis spread on variable rate, additional margin (percent)			3.50%
Eurodollar Rate | Second Lien Term Loan Facility 2018, Eurodollar Loans
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			8.75%
Eurodollar Rate | Second Lien Term Loan Facility 2018, Base Rate Loans
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			1.00%
Basis spread on variable rate, additional margin (percent)			7.75%
Federal Funds Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			0.50%
Federal Funds Rate | Second Lien Term Loan Facility 2018, Base Rate Loans
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			0.50%
Principal Amounts Prepaid Prior to First Anniversary | $75 million Second Lien Term Loan | Revolving Credit
Line of Credit Facility [Line Items]
Line of credit facility, periodic payment (percent)			2.00%
Principal Amounts Prepaid After First Anniversary | $75 million Second Lien Term Loan | Revolving Credit
Line of Credit Facility [Line Items]
Line of credit facility, periodic payment (percent)			1.00%
Maximum | Forecast
Line of Credit Facility [Line Items]
Required remittance of excess cash flow (percent)	50.00%
Loss On Extinguishment Of Debt | Credit Facility 2018
Line of Credit Facility [Line Items]
New debt issuance costs			$ 364,000
Previously incurred unamortized debt issuance costs or discount			3,571,000
Total			3,935,000
Capitalized And Amortized | Credit Facility 2018
Line of Credit Facility [Line Items]
New debt issuance costs			7,118,000
Previously incurred unamortized debt issuance costs or discount			348,000
Total			$ 7,466,000
Interest Rate Swaps | Cash Flow Hedging
Line of Credit Facility [Line Items]
Number of interest rate swap agreements | agreement				2	2
Aggregate notional amount				$ 185,300,000	$ 185,300,000