Note 4 - Investment Securities (Details Textual) - USD ($)	1 Months Ended	3 Months Ended	6 Months Ended
	Oct. 07, 2015	Aug. 29, 2015	Aug. 29, 2015	Feb. 28, 2015
Auction Rate Securities [Member] | Interest Expense [Member]
Available-for-sale Securities, Gross Realized Gain (Loss)		$ (1,800,000)	$ (1,800,000)
Auction Rate Securities [Member]
Available-for-sale Securities, Current		28,900,000	28,900,000
Available-for-sale Securities, Short-term Investments, Amortized Cost		$ 30,700,000	$ 30,700,000
Available-for-Sale Securities, Current, Percentage of Par Value		94.00%	94.00%
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	$ 28,900,000
Available-for-sale Securities, Long-term Investments, Amortized Cost		$ 20,300,000	$ 20,300,000	$ 51,000,000
Available-for-sale Securities Temporary Impairment Adjustment Accumulated Other Comprehensive Income (Loss)		1,100,000	1,100,000	3,100,000
US Treasury Securities [Member]
Held-to-maturity Securities, Current		0	0	110,000,000
Other Trading Investment Securities [Member]
Deferred Compensation Plan Assets		$ 51,300,000	$ 51,300,000	49,200,000
Held-to-maturity Securities, Current				110,000,000
Available-for-sale Securities, Current		$ 28,900,000	$ 28,900,000	0
Deferred Compensation Plan Assets		$ 51,300,000	$ 51,300,000	$ 49,200,000