Gulf Island Fabrication, Inc. Annual report pursuant to Section 13 and 15(d)

Annual report pursuant to Section 13 and 15(d)

Revenue, Contract Assets and Liabilities and Other Contract Matters - Additional Information (Details)

Revenue, Contract Assets and Liabilities and Other Contract Matters - Additional Information (Details) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) vessel ship Vechicle	Dec. 31, 2019 USD ($) vessel Vechicle Project	Dec. 31, 2018 USD ($)	Mar. 31, 2021 USD ($) vessel	Mar. 31, 2018 vessel
Long Term Contracts Or Programs Disclosure [Line Items]
Reduction of estimated contract price for liquidated damages, amount			$ 0.6	$ 12.9
Number of multi-purpose service vessels \| vessel			2	2			2
Contract asset under dispute, noncurrent			$ 12.5	$ 12.5
Reversal of gross profit recognized		$ 2.5
Number of towing, salvage and rescue vessels \| ship			5
Hurricane Laura
Long Term Contracts Or Programs Disclosure [Line Items]
Date of landfall			2020-08
Impact of Hurricane Laura, description			In August 2020, Hurricane Laura made landfall as a high-end Category 4 hurricane in Lake Charles, Louisiana, where its high winds and flooding caused significant damage throughout the region. At our Lake Charles Yard, Hurricane Laura primarily damaged drydocks, warehouses, bulkheads and our ninth harbor tug project which was nearing completion and subsequently completed in the fourth quarter 2020.
Total charges related to deductibles			$ 1.3
Deductible charges associated with, description			As a result, during 2020, we recorded charges of $1.3 million related to deductibles associated with our builder’s risk, equipment, property and marine liability insurance coverages, and our preliminary estimates of cost associated with uninsurable damage, primarily for bulkheads.
Shipyard
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			$ 16.6	12.3	$ 2.4
F&S
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			2.7	4.9	6.7
Contracts For Construction
Long Term Contracts Or Programs Disclosure [Line Items]
Reduction of estimated contract price for liquidated damages, amount				11.2
Towing, Salvage and Rescue Ship
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			$ 7.3
Number of vehicle ferry projects \| Vechicle			5
Reserve for loss			$ 3.2
Number of towing, salvage and rescue vessels \| ship			5
Number of additional vessels constructed upon exercise of option \| vessel			3
Towing, Salvage and Rescue Ship \| Scenario Forecast
Long Term Contracts Or Programs Disclosure [Line Items]
Number of additional vessels construction not exercised under contract \| vessel						3
Contractual obligation						$ 13.1
Towing, Salvage and Rescue Ship \| Minimum
Long Term Contracts Or Programs Disclosure [Line Items]
Projects, percent complete (percentage)			10.00%
Towing, Salvage and Rescue Ship \| Maximum
Long Term Contracts Or Programs Disclosure [Line Items]
Projects, percent complete (percentage)			60.00%
Harbor Tug
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			$ 1.0	4.9	6.7
Number of vehicle ferry projects \| Vechicle			2
Reserve for loss				1.6
Forty-Vehicle Ferry
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			$ 7.2	$ 5.1
Number of vehicle ferry projects \| Vechicle			2	2
Reserve for loss			$ 4.8	$ 3.0
Incremental forecast costs	$ 4.1
Forty-Vehicle Ferry \| Other (Income) Expense, Net
Long Term Contracts Or Programs Disclosure [Line Items]
Accrued deductible on insurance coverage	$ 0.1
Forty-Vehicle Ferry \| Minimum
Long Term Contracts Or Programs Disclosure [Line Items]
Incremental forecast costs			1.0
Forty-Vehicle Ferry \| Maximum
Long Term Contracts Or Programs Disclosure [Line Items]
Incremental forecast costs			4.0
First Forty-Vehicle Ferry
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			6.2
Second Forty-Vehicle Ferry Project
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			$ 1.0
Projects, percent complete (percentage)			80.00%
Seventy-Vehicle Ferry
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			$ 1.1
Projects, percent complete (percentage)			55.00%
Reserve for loss			$ 0.5
Jacket and Deck
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			1.2	2.0
Reserve for loss				1.1
Paddlewheel Riverboat and Subsea Components Projects
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins			$ 1.5
Ice-Breaker Tug
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins				1.5
Reserve for loss				0.1
Research Vessel Projects
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins				$ 0.8
Number of Research Vessels Projects \| Project				3
Paddle Wheel River Boat
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins				$ 1.3
Reserve for loss				0.2
Subsea Components Project
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins				1.6
Reserve for loss				$ 0.2
Petrochemical Modules
Long Term Contracts Or Programs Disclosure [Line Items]
Change in estimated margins					$ 2.4