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           Dividend (Details) (Subsequent events, USD $) 
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        0 Months Ended | 
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           Apr. 03, 2015 
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           Subsequent events 
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| Subsequent events | |
| Cash dividend declared (in dollars per share) | 
$ 0.045us-gaap_CommonStockDividendsPerShareDeclared / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember  | 
      
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- Definition 
          Aggregate dividends declared during the period for each share of common stock outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Details 
          
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