INDEBTEDNESS (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended
	Feb. 28, 2017	May 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2014
Long-term Debt, Gross			$ 143,750		$ 143,750		$ 143,750
Debt Instrument, Unamortized Discount			17,328		17,328		20,644
Line of Credit Facility, Maximum Borrowing Capacity	$ 40,000
Deferred Finance Costs, Net			2,041		2,041		2,463
Interest Income (Expense), Nonoperating, Net			(3,025)	$ (2,830)	(5,957)	$ (5,612)
Long-term Line of Credit			30,000		30,000
Proceeds from Lines of Credit	$ 30,000				30,000	0
Prepaid Expenses and Other Current Assets [Member]
Deferred Costs, Current			$ 200		$ 200
Convertible Senior Notes [Member]
Long-term Debt, Gross								$ 143,800
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate								3.00%
Debt Instrument, Unamortized Discount								$ 33,600
Class of Warrant or Right, Exercise Price of Warrants or Rights								$ 96.21
Debt Instrument, Interest Rate, Effective Percentage			7.90%		7.90%
Debt Instrument, Convertible, Conversion Price								$ 69.48
Convertible Senior Notes [Member] | Accrued Liabilities [Member]
Interest Payable, Current			$ 400		$ 400		$ 400
Line of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity		$ 30,000
Debt Instrument, Maturity Date		May 12, 2019
Line of Credit Facility, Commitment Fee Percentage		0.25%
Debt Instrument, Description of Variable Rate Basis		LIBOR rate plus 1.25%, 1.50%, or 1.75% per annum, depending upon availability under the Citizens Agreement, or an alternative base rate plus either 0.25%, 0.50%, or 0.75% per annum
Deferred Finance Costs, Net				$ 300		$ 300
Interest Income (Expense), Nonoperating, Net			$ 200		$ 300
Line Of Credit Facility Additional Revolving Commitment		$ 10,000