Annual report pursuant to Section 13 and 15(d)

LONG-TERM DEBT (Schedule of Debt Interest Expense) (Details)

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LONG-TERM DEBT (Schedule of Debt Interest Expense) (Details) - 2.5% Convertible Senior Notes Due 2019 [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Debt Instrument [Line Items]      
Interest rate, stated percentage 2.50% 2.50% 2.50%
Contractual interest coupon $ 6,875 $ 6,875 $ 6,856
Amortization of debt discount 5,080 4,833 4,599
Amortization of debt issuance costs 1,358 1,358 1,355
Total interest cost recognized on the notes $ 13,313 $ 13,066 $ 12,810