Note 3 - Financing Arrangements (Detail) (USD $) In Millions, unless otherwise specified		12 Months Ended			1 Months Ended				1 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Scenario, Forecast [Member] Line of Credit [Member]	Dec. 31, 2012 Senior Debt Obligations [Member] Line of Credit [Member]	Dec. 31, 2011 Senior Debt Obligations [Member] Line of Credit [Member]	Mar. 31, 2014 Senior Debt Obligations [Member] Loans Payable [Member]	Mar. 31, 2013 Senior Debt Obligations [Member] Loans Payable [Member]	Dec. 31, 2012 Senior Debt Obligations [Member] Loans Payable [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes First Issuance [Member]	Jul. 31, 2013 Senior Notes [Member] Required Installment Payment [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes Second Issuance [Member]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 100.0
Long-term Debt, Maturities, Repayments of Principal in Year Two	250.0
Long-term Debt, Maturities, Repayments of Principal in Year Three	249.5
Long-term Debt, Maturities, Repayments of Principal in Year Four	85.8
Line of Credit Facility, Maximum Borrowing Capacity			500
Line of Credit Facility, Increase, Additional Borrowings		250
Line of Credit Facility, Amount Outstanding			85.8	99.8
Debt, Weighted Average Interest Rate			2.03%				1.26%
Unsecured Debt							200	150		250
Debt Instrument, Periodic Payment, Principal					150	50
Debt Instrument, Interest Rate, Stated Percentage								6.08%		3.375%
Repayments of Unsecured Debt									$ 50