Investments, At Equity, And Advances To 50% Or Less Owned Companies	9 Months Ended
Sep. 30, 2017
Equity Method Investment, Summarized Financial Information [Abstract]
Investments, At Equity, And Advances To 50% Or Less Owned Companies	CFCo. SCFCo was established to operate inland river towboats and inland river dry-cargo barges on the Parana-Paraguay Rivers in South America and a terminal facility at Port Ibicuy, Argentina. During the nine months ended September 30, 2017, the Company and its partner each contributed capital of $0.4 million and made working capital advances of $0.5 million to SCFCo, received working capital repayments of $1.7 million from SCFCo and converted $4.2 million of loans to capital. As of September 30, 2017, the Company had outstanding loans and working capital advances to SCFCo of $27.4 million. Trailer Bridge. Trailer Bridge is an operator of U.S.-flag deck and RORO barges and provides marine transportation services between Jacksonville, Florida, San Juan, Puerto Rico and Puerto Plata, Dominican Republic. The Company provides secured financing to Trailer Bridge and, during the nine months ended September 30, 2017, the Company provided advances of $2.0 million to Trailer Bridge and received repayments of $2.1 million from Trailer Bridge on the secured financing. As of September 30, 2017, the outstanding amount on the secured financing was $3.9 million, inclusive of accrued and unpaid interest. SeaJon. SeaJon owned an articulated tug-barge operating in the Great Lakes trade that was sold to a third party in June 2017. During the nine months ended September 30, 2017, the Company received dividends of $12.5 million and capital distributions of $3.5 million from SeaJon. Kotug. On April 1, 2017, the Company and Kotug Caribbean Holdings LLC formed Kotug Seabulk Maritime LLC (“Kotug”) to operate four foreign-flag harbor tugs and one foreign-flag ocean liquid tank barge in Freeport, Grand Bahama. The Company has a 50% ownership interest in Kotug. During the nine months ended September 30, 2017, the Company and its partner each contributed capital of $0.3 million. RF Vessel Holdings. On July 3, 2017, ISH emerged from bankruptcy pursuant to its chapter 11 plan of reorganization and SEACOR Ocean Transport Inc., a wholly-owned subsidiary of SEACOR, acquired all of the equity of the reorganized ISH (see Note 2). As part of the ISH business acquisition, the Company acquired a 100% interest in Rail-Ferry Vessel Holdings LLC (“RF Vessel Holdings”), which owns two foreign-flag rail ferries. On September 1, 2017, the Company sold a 50% interest in RF Vessel Holdings to G&W Agave Holdings (MI) Inc. for $1.9 million and retained a 50% ownership interest in the newly-formed joint venture. Golfo de Mexico. On July 3, 2017, ISH emerged from bankruptcy pursuant to its chapter 11 plan of reorganization and SEACOR Ocean Transport Inc., a wholly-owned subsidiary of SEACOR, acquired all of the equity of the reorganized ISH (see Note 2). As part of the ISH business acquisition, the Company acquired a 100% interest in Golfo de Mexico Rail-Ferry Holdings LLC (“Golfo de Mexico”), which operates the two foreign-flag rail ferries owned by RF Vessel Holdings. On September 1, 2017, the Company sold a 50% interest in Golfo de Mexico to G&W Agave Holdings (MI) Inc. for $3.1 million and retained a 50% ownership interest in the newly-formed joint venture. VA&E. VA&E primarily focuses on the global origination, trading and merchandising of sugar, pairing producers and buyers and arranging for the transportation and logistics of the product. The Company provides an uncommitted credit facility of up to $3.5 million and a subordinated loan of $3.5 million to VA&E. During the nine months ended September 30, 2017, VA&E borrowed $3.5 million on the credit facility. As of September 30, 2017, the outstanding balance on the credit facility and subordinated loan was $7.5 million, inclusive of accrued and unpaid interest. During the nine months ended September 30, 2017, the Company identified indicators of impairment for its investment in VA&E based on their recent financial results and recognized an impairment charge of $0.9 million, net of tax, for an other-than-temporary decline in the fair value of its investment in VA&E (see Note 8). Avion. Avion is a distributor of aircraft and aircraft related parts. During the nine months ended September 30, 2017, the Company made advances of $1.0 million to Avion and received repayments of $2.0 million from Avion. As of September 30, 2017, the Company had outstanding advances to Avion of $2.0 million.

CFCo. SCFCo was established to operate inland river towboats and inland river dry-cargo barges on the Parana-Paraguay Rivers in South America and a terminal facility at Port Ibicuy, Argentina. During the nine months ended September 30, 2017, the Company and its partner each contributed capital of $0.4 million and made working capital advances of $0.5 million to SCFCo, received working capital repayments of $1.7 million from SCFCo and converted $4.2 million of loans to capital. As of September 30, 2017, the Company had outstanding loans and working capital advances to SCFCo of $27.4 million.

Trailer Bridge. Trailer Bridge is an operator of U.S.-flag deck and RORO barges and provides marine transportation services between Jacksonville, Florida, San Juan, Puerto Rico and Puerto Plata, Dominican Republic. The Company provides secured financing to Trailer Bridge and, during the nine months ended September 30, 2017, the Company provided advances of $2.0 million to Trailer Bridge and received repayments of $2.1 million from Trailer Bridge on the secured financing. As of September 30, 2017, the outstanding amount on the secured financing was $3.9 million, inclusive of accrued and unpaid interest.

SeaJon. SeaJon owned an articulated tug-barge operating in the Great Lakes trade that was sold to a third party in June 2017. During the nine months ended September 30, 2017, the Company received dividends of $12.5 million and capital distributions of $3.5 million from SeaJon.

Kotug. On April 1, 2017, the Company and Kotug Caribbean Holdings LLC formed Kotug Seabulk Maritime LLC (“Kotug”) to operate four foreign-flag harbor tugs and one foreign-flag ocean liquid tank barge in Freeport, Grand Bahama. The Company has a 50% ownership interest in Kotug. During the nine months ended September 30, 2017, the Company and its partner each contributed capital of $0.3 million.

RF Vessel Holdings. On July 3, 2017, ISH emerged from bankruptcy pursuant to its chapter 11 plan of reorganization and SEACOR Ocean Transport Inc., a wholly-owned subsidiary of SEACOR, acquired all of the equity of the reorganized ISH (see Note 2). As part of the ISH business acquisition, the Company acquired a 100% interest in Rail-Ferry Vessel Holdings LLC (“RF Vessel Holdings”), which owns two foreign-flag rail ferries. On September 1, 2017, the Company sold a 50% interest in RF Vessel Holdings to G&W Agave Holdings (MI) Inc. for $1.9 million and retained a 50% ownership interest in the newly-formed joint venture.

Golfo de Mexico. On July 3, 2017, ISH emerged from bankruptcy pursuant to its chapter 11 plan of reorganization and SEACOR Ocean Transport Inc., a wholly-owned subsidiary of SEACOR, acquired all of the equity of the reorganized ISH (see Note 2). As part of the ISH business acquisition, the Company acquired a 100% interest in Golfo de Mexico Rail-Ferry Holdings LLC (“Golfo de Mexico”), which operates the two foreign-flag rail ferries owned by RF Vessel Holdings. On September 1, 2017, the Company sold a 50% interest in Golfo de Mexico to G&W Agave Holdings (MI) Inc. for $3.1 million and retained a 50% ownership interest in the newly-formed joint venture.

VA&E. VA&E primarily focuses on the global origination, trading and merchandising of sugar, pairing producers and buyers and arranging for the transportation and logistics of the product. The Company provides an uncommitted credit facility of up to $3.5 million and a subordinated loan of $3.5 million to VA&E. During the nine months ended September 30, 2017, VA&E borrowed $3.5 million on the credit facility. As of September 30, 2017, the outstanding balance on the credit facility and subordinated loan was $7.5 million, inclusive of accrued and unpaid interest. During the nine months ended September 30, 2017, the Company identified indicators of impairment for its investment in VA&E based on their recent financial results and recognized an impairment charge of $0.9 million, net of tax, for an other-than-temporary decline in the fair value of its investment in VA&E (see Note 8).

Avion. Avion is a distributor of aircraft and aircraft related parts. During the nine months ended September 30, 2017, the Company made advances of $1.0 million to Avion and received repayments of $2.0 million from Avion. As of September 30, 2017, the Company had outstanding advances to Avion of $2.0 million.