Note 6 - Fair Value Measurements - Estimated Fair Value of Senior Notes (Details) (Parentheticals)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Senior Notes 5.625% Due February 2020 [Member]
Interest rate	5.625%	5.625%
Maturity date	Feb. 29, 2020	Feb. 29, 2020
Senior Notes 5.5% Due January 2024 [Member]
Interest rate	5.50%	5.50%
Maturity date	Jan. 31, 2024	Jan. 31, 2024
Senior Notes 6% Due January 2043 [Member]
Interest rate	6.00%	6.00%
Maturity date	Jan. 31, 2043	Jan. 31, 2043