Note 11 - Revolving Credit Facility and Letter of Credit Facilities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
Cash Collateral Deposits	$ 25.0
Unsecured Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	210
Aggregate Borrowing Commitment	400
Line of Credit Facility, Current Borrowing Capacity	203.5
Letter of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity	11
Letters of Credit Outstanding, Amount	7.2
Uncommitted Letter of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity	30
Letters of Credit Outstanding, Amount	$ 17.4