Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity At-the-Market Offering (Details)

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Stockholders' Equity At-the-Market Offering (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2014
Class of Stock [Line Items]    
At-the-Market Offering, Number of Shares Authorized to be Sold   20,000,000two_AtMarketOfferingNumberOfSharesAuthorizedToBeSold
Stock Issued And Outstanding, Shares, At-the-Market Offering   7,585,869two_StockIssuedAndOutstandingSharesAtMarketOffering
Stock Issued and Outstanding, Value, At-the-Market Offering   $ 77,603two_StockIssuedAndOutstandingValueAtMarketOffering
Stock Issued During Period, Shares, At The Market Offering 7,585,869two_StockIssuedDuringPeriodSharesAtTheMarketOffering  
Stock Issued During Period, Value, At The Market Offering $ 77,603two_StockIssuedDuringPeriodValueAtTheMarketOffering