Note 6 - Employee Stock Benefit Plans - Equity-based Performance Stock Units (Details)	12 Months Ended
	Dec. 31, 2016
Equity-based Performance Stock Units Granted in 2016 [Member]
Performance Criteria Period (Year)	3 years
Equity-based Performance Stock Units Granted in 2016 [Member] | Minimum [Member]
Range of Award	25.00%
Equity-based Performance Stock Units Granted in 2016 [Member] | Maximum [Member]
Range of Award	200.00%
Equity-based Performance Stock Units Granted in 2015 [Member]
Performance Criteria Period (Year)	2 years
Equity-based Performance Stock Units Granted in 2015 [Member] | Minimum [Member]
Range of Award	25.00%
Equity-based Performance Stock Units Granted in 2015 [Member] | Maximum [Member]
Range of Award	200.00%
Equity-based Performance Stock Units Granted in 2014 [Member]
Performance Criteria Period (Year)	2 years
Equity-based Performance Stock Units Granted in 2014 [Member] | Minimum [Member]
Range of Award	0.00%
Equity-based Performance Stock Units Granted in 2014 [Member] | Maximum [Member]
Range of Award	150.00%