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Significant Accounting Policies (Schedule Of Redeemable Capital Shares) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Significant Accounting Policies [Abstract]      
Opening balance (in Shares) 7,800,000 8,750,000 11,750,000
Creations (in Shares) 250,000 50,000 150,000
Redemptions (in Shares) (700,000) (1,000,000) (3,150,000)
Closing balance (in Shares) 7,350,000 7,800,000 8,750,000
Opening balance   $ 1,033,745 $ 1,930,056
Creations $ 30,185 [1] 6,437 [1] 22,226
Redemptions $ (75,998) [1] $ (118,407) [1] (418,671)
Adjustment to redemption value [1]     (499,866)
Closing balance     $ 1,033,745
Redemption value per Share at period end (in Dollars per share)     $ 118.14
[1] Effective January 1, 2014, the Trust has adopted the provisions of Topic 946. Refer to Note 2.1 for additional information.