Statements of Changes in Shareholders' Equity (Deficit) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shareholders' equity (deficit) - beginning of period	$ (1,511,462)	$ (5,105,181)	$ (975,307)
Net income	390,140	3,070,085	234,419
Adjustment of redeemable capital Shares to redemption value	(454,637)	523,634	(4,364,293)
Shareholders' equity (deficit) - end of period	$ (1,575,959)	$ (1,511,462)	$ (5,105,181)