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Convertible debt (Details) $ / shares in Units, $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2015 USD ($) | Jun. 30, 2015 USD ($) $ / shares | Jun. 30, 2014 USD ($) | Dec. 31, 2014 USD ($)
Debt Instrument [Line Items] |  |  |  |
Debt Issuance Cost |  | $ (408) | $ 0 |
Convertible debt, issuance cost, equity component |  | $ 1,200 |  |
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate | 2.00% | 2.00% |  |
Debt Instrument, Convertible, Conversion Ratio |  | 29.5972 |  |
Debt Instrument, Convertible, Stock Price Trigger | $ / shares |  | $ 33.79 |  |
Interest Expense, Debt | $ 2,223 | $ 4,408 |  |
Debt Instrument, Fair Value Disclosure | 110,391 | 110,391 |  |
Debt Instrument, Face Amount | 143,800 | 143,800 |  | $ 143,800
Debt Instrument, Periodic Payment, Interest | 719 | 1,438 |  |
Amortization of Debt Discount (Premium) | 1,306 | 2,577 |  |
Debt Instrument, Unamortized Discount (Premium), Net | (30,389) | (30,389) |  | (33,302)
Convertible Debt, Noncurrent | 113,361 | 113,361 |  | 110,448
Debt Instrument, Convertible, Carrying Amount of Equity Component | 28,714 | $ 28,714 |  | 28,714
Purchase of convertible bond hedge |  |  |  | (29,411)
Investment Warrants, Exercise Price | $ / shares |  | $ 45.48 |  |
Proceeds from Issuance of Warrants |  |  |  | $ 17,106
Convertible Debt [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt Issuance Cost |  | $ 4,300 |  |
Amortization of Financing Costs | $ 198 | $ 393 |  |

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- Definition Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.8) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
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- Definition Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.8) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 8 -Article 9 + Details
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