Note 13 - Notes Payable - Senior Unsecured Notes Issuance (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)
Senior Unsecured Notes 1 [Member]
Date Issued	Nov-16
Maturity Date	Mar-24
Amount Issued	$ 400,000,000
Interest Rate	2.70%
Senior Unsecured Notes 2 [Member]
Date Issued	Nov-16
Maturity Date	Dec-46
Amount Issued	$ 350,000,000
Interest Rate	4.125%
Senior Unsecured Notes 3 [Member]
Date Issued	Aug-16
Maturity Date	Oct-26
Amount Issued	$ 500,000,000
Interest Rate	2.80%
Senior Unsecured Notes 4 [Member]
Date Issued	May-16
Maturity Date	Apr-45
Amount Issued	$ 150,000,000
Interest Rate	4.25%
Senior Unsecured Notes 5 [Member]
Date Issued	Oct-15
Maturity Date	Nov-22
Amount Issued	$ 500,000,000
Interest Rate	3.40%
Senior Unsecured Notes 6 [Member]
Date Issued	Mar-15
Maturity Date	Apr-45
Amount Issued	$ 350,000,000
Interest Rate	4.25%