Note 10 - Long-term Incentive Plan - Activity Pertaining to Phantom and Restricted Common Stock Unit Awards (Details) - Long-Term Incentive Plan [Member] - Phantom and Restricted Units Holders [Member]	9 Months Ended
	Sep. 30, 2019 $ / shares shares
Nonvested, number of units, beginning balance (in shares) | shares	998,219
Granted, number of units (in shares) | shares	571,165
Vested, number of units (in shares) | shares	366,282
Forfeited, number of units (in shares) | shares	104,758
Nonvested, number of units, ending balance (in shares) | shares	1,098,344
Nonvested, weighted average grant date fair value, beginning balance (in dollars per share) | $ / shares	$ 5.88
Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	1.14
Vested, weighted average grant date fair value (in dollars per share) | $ / shares	4.80
Forfeited, weighted average grant date fair value (in dollars per share) | $ / shares	4.10
Nonvested, weighted average grant date fair value, ending balance (in dollars per share) | $ / shares	$ 3.45