Fair Value Measurements (Non-Financial Assets And Liabilities Measured At Fair Value) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	$ 130,800,000	$ 7,100,000	$ 4,400,000
Equity Method Investment, Other than Temporary Impairment	14,700,000		$ 3,300,000
Provision for Loan and Lease Losses	8,500,000
Other Offshore Marine Services Joint Ventures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investment, Other than Temporary Impairment	500,000
Falcon Global [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investment, Other than Temporary Impairment	6,400,000
SCFCo Holdings [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges		21,500,000
Equity Method Investment, Other than Temporary Impairment	$ 7,700,000	21,500,000
Fair Value Inputs, Earnings before Interest, Taxes, Depreciation, and Amortization Multiple	7
SeaJon II [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Business Combination, Separately Recognized Transactions, Net Gains and Losses	$ 1,900,000
Offshore Support Vessels [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	120,800,000	6,600,000
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure	0
Cost Method Investments, Fair Value Disclosure	0
Equity Method Investments, Fair Value Disclosure	0	102,509,000
Notes Receivable, Fair Value Disclosure	0
Assets Held-for-sale, Long Lived, Fair Value Disclosure		0
Fair Value, Inputs, Level 1 [Member] | Offshore Support Vessels Anchor Handling Towing Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0
Fair Value, Inputs, Level 1 [Member] | Liftboats [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0
Fair Value, Inputs, Level 1 [Member] | Offshore Support Vessels Specialty [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0
Fair Value, Inputs, Level 1 [Member] | Other Property [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure	0
Cost Method Investments, Fair Value Disclosure	3,600,000
Equity Method Investments, Fair Value Disclosure	3,438,000	6,802,000
Notes Receivable, Fair Value Disclosure	0
Assets Held-for-sale, Long Lived, Fair Value Disclosure		200,000
Fair Value, Inputs, Level 2 [Member] | Offshore Support Vessels Anchor Handling Towing Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	2,600,000
Fair Value, Inputs, Level 2 [Member] | Liftboats [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0
Fair Value, Inputs, Level 2 [Member] | Offshore Support Vessels Specialty [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	4,000,000
Fair Value, Inputs, Level 2 [Member] | Other Property [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	3,003,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure	28,506,000
Cost Method Investments, Fair Value Disclosure	0
Equity Method Investments, Fair Value Disclosure	48,150,000	39,201,000
Notes Receivable, Fair Value Disclosure	11,900,000
Assets Held-for-sale, Long Lived, Fair Value Disclosure		0
Fair Value, Inputs, Level 3 [Member] | Offshore Support Vessels Anchor Handling Towing Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	$ 42,500,000
Fair Value Inputs, Comparability Adjustments	55.00%
Fair Value Inputs, Discount Rate	74.00%
Fair Value, Inputs, Level 3 [Member] | Liftboats [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	$ 62,830,000
Fair Value Inputs, Comparability Adjustments	42.00%
Fair Value Inputs, Discount Rate	61.00%
Fair Value, Inputs, Level 3 [Member] | Liftboats [Member] | Falcon Global [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Comparability Adjustments	25.00%
Fair Value, Inputs, Level 3 [Member] | Offshore Support Vessels Specialty [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	$ 0
Fair Value, Inputs, Level 3 [Member] | Other Property [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	$ 1,800,000
Fair Value Inputs, Comparability Adjustments	33.00%
Fair Value Inputs, Discount Rate	56.00%
Witt O'Brien's LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Impairment Loss	$ 19,600,000
Corporate And Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Provision for Loan and Lease Losses	6,700,000
Offshore Marine Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	119,700,000
Goodwill, Impairment Loss		$ 13,400,000
Provision for Loan and Lease Losses	1,800,000
Offshore Marine Services [Member] | Offshore Support Vessels Anchor Handling Towing Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	62,800,000
Offshore Marine Services [Member] | Offshore Support Vessels [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	3,600,000
Offshore Marine Services [Member] | Liftboats [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	19,900,000
Offshore Marine Services [Member] | Offshore Support Vessels Specialty [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	12,700,000
Finite-Lived Intangible Assets [Member] | Witt O'Brien's LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	10,000,000
Cost-method Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost-method Investments, Other than Temporary Impairment	11,600,000
Three Point Seven Five Percentage Convertible Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Embedded Derivative, Loss on Embedded Derivative	13,826,000
Cost Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Offshore Support Vessels Anchor Handling Towing Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	364,000,000
Cost Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Liftboats [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	$ 279,000,000