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Federal and State Income Taxes - Summary Cash Dividends Per Common Share for Individual Shareholder (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Auction Market Preferred Securities, Stock Series [Line Items]      
Cash dividends per Common Share $ 0.49us-gaap_CommonStockDividendsPerShareCashPaid $ 0.65us-gaap_CommonStockDividendsPerShareCashPaid $ 0.49us-gaap_CommonStockDividendsPerShareCashPaid
Ordinary Dividends [Member]      
Auction Market Preferred Securities, Stock Series [Line Items]      
Cash dividends per Common Share    $ 0.65us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_DividendsAxis
= us-gaap_DividendPaidMember		 $ 0.49us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_DividendsAxis
= us-gaap_DividendPaidMember
Capital Gains [Member]      
Auction Market Preferred Securities, Stock Series [Line Items]      
Cash dividends per Common Share $ 0.49us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_DividendsAxis
= fur_CapitalGainsMember		      
Nontaxable Distribution [Member]      
Auction Market Preferred Securities, Stock Series [Line Items]      
Cash dividends per Common Share