Supplemental Selected Quarterly Financial Data (Unaudited) - Supplemental Selected Quarterly Financial Data (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017	[1],[2]	Sep. 30, 2017	[1],[2]	Jun. 30, 2017	[1],[2]	Mar. 31, 2017	[1],[2]	Dec. 31, 2016	[2]	Sep. 30, 2016	[2]	Jun. 30, 2016	[2]	Mar. 31, 2016	[2]	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information [Line Items]
Vessel revenues	$ 56,241		$ 53,666		$ 37,426		$ 44,079		$ 41,879		$ 51,927		$ 53,673		$ 76,820		$ 191,412	$ 224,299	$ 476,070
Operating Income (Loss)	(14,278)		(16,667)		(31,318)		(26,481)		(27,484)		(14,445)	[3]	(21,510)		(780)	[3]	(88,744)	(64,219)	143,544
Net Income (loss)	$ 93,758		$ (18,950)		$ (19,489)		$ (27,898)		$ (19,243)		$ (16,503)		$ (20,586)		$ (7,514)		$ 27,421	$ (63,846)	$ 66,821	[4]
Earnings (loss) per common share:
Basic earnings (loss) per common share	$ 2.53		$ (0.51)		$ (0.53)		$ (0.76)		$ (0.53)		$ (0.45)		$ (0.57)		$ (0.21)		$ 0.74	$ (1.76)	$ 1.87
Diluted earnings (loss) per common share, in dollars per share	$ 2.48		$ (0.51)		$ (0.53)		$ (0.76)		$ (0.53)		$ (0.45)		$ (0.57)		$ (0.21)		$ 0.73	$ (1.76)	$ 1.84

[1] Results for the fiscal years 2017 and 2016 were significantly impacted by a drop in oil price, which resulted in reductions in both the Company's dayrates and utilization. In recognition of these weak market conditions, the Company elected to stack OSVs and MPSVs on various dates during fiscal 2017 and 2016. The Company had an average of 42.8 OSVs and 0.8 MPSVs stacked during the year ended December 31, 2017. The Company had an average of 41.3 OSVs and 0.3 MPSVs stacked during fiscal 2016.

[2] The sum of the four quarters may not equal annual results due to rounding.

[3] The results for the three months ended December 31, 2017 were favorably impacted by tax reform that was enacted in December 2017. As a result of tax reform, the Company recorded a benefit of $125,225 related to the repricing of its deferred tax liabilities. Such benefits were reduced primarily by tax expense related to credits that may not be utilized prior to their expiration. Excluding these one-time tax items from the Company's fourth quarter results its net loss would have been $(17,281) or $(0.47) per diluted share. See Note 9 for further information.

[4] The Company's net income for 2017 was favorably impacted by U.S. tax reform legislation that was enacted in December 2017. As a result of tax reform, the Company recorded a benefit of $125,225 related to the repricing of its deferred tax liabilities. Such benefits were reduced primarily by tax expense related to credits that may not be utilized prior to their expiration. Excluding these one-time tax items from the Company's December 31, 2017 results, its net loss would have been $(82,687) or $(2.24) per diluted share for the year ended December 31, 2017. See Note 9 for further information.