Note 13 - Unaudited Quarterly Financial Data - Summarized Quarterly Financial Data (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Marine Services Revenue	$ 50,585,000	$ 60,668,000	$ 74,461,000	$ 89,092,000	$ 116,118,000	$ 128,686,000	$ 131,365,000	$ 119,600,000	$ 274,806,000	$ 495,769,000	$ 454,604,000
Operating income	(11,706,000)	(167,081,000)	(4,207,000)	(558,000)	20,740,000	34,791,000	22,890,000	23,244,000	(183,552,000)	101,665,000	100,476,000
Net income	$ (16,638,000)	$ (185,226,000)	$ (8,245,000)	$ (5,126,000)	$ 7,275,000	$ 24,344,000	$ 14,199,000	$ 16,557,000	$ (215,235,000)	$ 62,375,000	$ 70,606,000
Per share (basic) (in dollars per share)	$ (0.67)	$ (7.48)	$ (0.33)	$ (0.21)	$ 0.29	$ 0.92	$ 0.54	$ 0.63	$ (8.70)	$ 2.39	$ 2.70
Per share (diluted) (in dollars per share)	$ (0.67)	$ (7.48)	$ (0.33)	$ (0.21)	$ 0.29	$ 0.92	$ 0.54	$ 0.63	$ (8.70)	$ 2.39	$ 2.70