Statements Of Changes In Shareholders' Equity (Deficit) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Statements Of Changes In Shareholders' Equity (Deficit) [Abstract]
Shareholders' equity (deficit) - beginning of period	$ (1,846,637)	$ (1,748,981)	$ (1,748,981)
Net income	16,992	96,018	258,847
Adjustment of redeemable capital Shares to redemption value	(697,360)		(356,503)
Shareholders' equity (deficit) - end of period	$ (2,527,005)		$ (1,846,637)