Note 7 - Investments Investments In Any Person And Its Affiliates That Exceed 10% of Total Stockholders' Equity (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Investment Holdings [Line Items]
Trading Securities	$ 4,211,059,000	$ 4,562,821,000
Short-term Investments	1,261,703,000	1,537,498,000
Total	5,783,559,000	6,628,883,000
BlackRock Liquidity Funds T-Fund Money Market [Member] [Member] | Investments in Any Person and Its Affiliates That Exceed 10 Percent of Total Stockholders Equity [Member]
Investment Holdings [Line Items]
Trading Securities	0
Short-term Investments	173,378,000
Total	173,378,000
Fidelity Treasury Only Money Market [Member] [Member] | Investments in Any Person and Its Affiliates That Exceed 10 Percent of Total Stockholders Equity [Member]
Investment Holdings [Line Items]
Trading Securities	0
Short-term Investments	167,631,000
Total	167,631,000
Federated Treasury Only Obligations Money Market [Member] | Investments in Any Person and Its Affiliates That Exceed 10 Percent of Total Stockholders Equity [Member]
Investment Holdings [Line Items]
Trading Securities	0
Short-term Investments	139,000,000
Total	139,000,000
State of Illinois [Member] | Investments in Any Person and Its Affiliates That Exceed 10 Percent of Total Stockholders Equity [Member]
Investment Holdings [Line Items]
Trading Securities	129,672,000
Short-term Investments	0
Total	129,672,000
Invesco-AIM Advisors STIT Treasury PTF Money Market [Member] | Investments in Any Person and Its Affiliates That Exceed 10 Percent of Total Stockholders Equity [Member]
Investment Holdings [Line Items]
Trading Securities	0
Short-term Investments	129,000,000
Total	129,000,000
Total Investments in Any Person and Its Affiliates That Exceed 10% of Total Stockholders Equity [Member] | Investments in Any Person and Its Affiliates That Exceed 10 Percent of Total Stockholders Equity [Member]
Investment Holdings [Line Items]
Trading Securities	129,672,000
Short-term Investments	609,009,000
Total	$ 738,681,000