DEBT - 2017 Credit Facility (Details)		3 Months Ended		9 Months Ended
	Apr. 04, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) d	Sep. 30, 2016 USD ($)	Jul. 21, 2014
Term Loan Facility 2017 [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity, revolving credit facility	$ 135,000,000
Proceeds from lines of credit	135,000,000
Line of credit outstanding		$ 133,000,000		$ 133,000,000
Revolving Loan Facility 2017 [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity, revolving credit facility	50,000,000
Proceeds from lines of credit	$ 10,000,000
Line of credit outstanding		0		0
Available borrowing capacity		50,000,000		50,000,000
Credit Facility 2017 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Debt instrument, term	5 years
Debt instrument term, alternative to anniversary of closing date, period prior to maturity of another debt instrument	180 days
Minimum interest coverage ratio of consolidated EBITDA to consolidated interest expense	300.00%
Debt issuance costs	$ 5,000,000
Interest expense		2,100,000		4,500,000
Amortization of debt issuance costs		200,000		500,000
Federal Funds Effective Swap Rate [Member] | Credit Agreement 2017, Base Rate Loans [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Eurodollar [Member] | Credit Agreement 2017, Eurodollar Loans [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.75%
Eurodollar [Member] | Credit Agreement 2017, Base Rate Loans [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Basis spread on variable rate, additional margin	2.75%
Convertible Debt [Member] | Convertible Senior 2019 Notes [Member]
Line of Credit Facility [Line Items]
Long-term Debt		137,300,000		$ 137,300,000
Debt Instrument, Convertible, Threshold Consecutive Trading Days | d				30
Interest rate per annum						2.50%
Amortization of debt issuance costs		$ 200,000	$ 200,000	$ 700,000	$ 700,000
Line of Credit, Payment Period One [Member] | Credit Facility 2017 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit facility, quarterly payment percent	1.25%
Line of Credit, Payment Period Two [Member] | Credit Facility 2017 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit facility, quarterly payment percent	1.875%
Line of Credit, Payment Period Three [Member] | Credit Facility 2017 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit facility, quarterly payment percent	2.50%
Line of Credit Facility, Covenant Period One [Member] | Credit Facility 2017 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Required maximum leverage ratio of consolidated total indebtedness to consolidated EBITDA	550.00%
Line of Credit Facility, Covenant Period Two [Member] | Credit Facility 2017 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Required maximum leverage ratio of consolidated total indebtedness to consolidated EBITDA	500.00%
Line of Credit Facility, Covenant Period Three [Member] | Credit Facility 2017 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Required maximum leverage ratio of consolidated total indebtedness to consolidated EBITDA	450.00%