Financial Highlights (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net Asset Value:
Net asset value per share-beginning of period	$ 23.55	$ 28.02	$ 23.21	$ 26.74
Net investment income (loss)	$ (0.09)	$ (0.10)	$ (0.18)	$ (0.20)
Net realized and unrealized gain (loss)	$ (1.59)	$ (1.51)	$ (0.73)	$ (0.30)
Distributions	$ (0.44)	$ (0.44)	$ (0.87)	$ (0.87)
Net asset value per share-end of period	$ 21.43	$ 25.97	$ 21.43	$ 25.97
Market Value:
Market value per share-beginning of period	$ 23.08	$ 27.26	$ 20.30	$ 25.80
Market value per share-end of period	$ 20.40	$ 26.25	$ 20.40	$ 26.25
Ratios to Average Net Assets:
Net investment income (loss)	(1.67%)	(1.48%)	(1.61%)	(1.46%)
Expenses	1.78%	1.60%	1.72%	1.61%
Total Returns:
Based on Net Asset Value	(7.17%)	(5.82%)	(4.10%)	0.25%
Based on Market Value	(9.74%)	(2.15%)	4.55%	5.03%