CONVERTIBLE SENIOR NOTES (Details)
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12 Months Ended |
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Apr. 07, 2011
USD ($)
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Dec. 31, 2017
USD ($)
$ / shares
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Dec. 31, 2016
USD ($)
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Dec. 31, 2015
USD ($)
$ / shares
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Dec. 31, 2011
USD ($)
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Mar. 15, 2011
USD ($)
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| CONVERTIBLE SENIOR NOTES [Line Items] |
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| Cash used for repurchase of debt |
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$ 0
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$ 25,931,219
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$ 54,376,600
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| Net gain repurchase of debt |
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0
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212,056
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13,693,269
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| Amortization of deferred convertible notes issuance costs and premium |
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$ 0
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32,935
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764,527
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| Convertible Senior Notes due 2018 [Member] |
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| CONVERTIBLE SENIOR NOTES [Line Items] |
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| Debt issued |
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$ 175,000,000
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| Interest rate (as a percent) |
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4.125%
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| Redemption price at the option of the holder as a percentage of principal amount together with any accrued but unpaid interest |
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100.00%
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| Repurchase of debt |
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26,145,000
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68,454,000
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$ 88,384,000
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| Cash used for repurchase of debt |
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25,931,219
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54,376,600
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57,055,127
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| Net gain repurchase of debt |
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212,056
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13,693,269
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28,349,939
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| Maximum aggregate principal amount pertaining to exercise of over-allotment of debt by initial purchasers |
$ 25,000,000
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$ 100
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| Deferred issuance cost expensed |
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1,725
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$ 384,131
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2,978,934
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| Refund of portion of premium paid due to repurchase of debt |
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861,280
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| Amortization of deferred convertible notes issuance costs and premium |
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$ 32,935
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$ 764,527
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| Debt Issuance Cost |
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$ 7,156,101
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| Convertible Senior Notes due 2018 [Member] | American Depository Shares (ADS) [Member] |
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| CONVERTIBLE SENIOR NOTES [Line Items] |
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| Conversion price of debts (in pound sterling per share/in dollars per ADS) | $ / shares |
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$ 10.5473
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| Number of shares to be allotted and issued on full conversion of debts (in shares/ADS) |
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2,478,833
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| Cap price (in dollars per ADS) | $ / shares |
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$ 15.0675
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| Premium of preliminary option |
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$ 21,504,779
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| Premium of over-allotment option |
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$ 3,197,500
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