Basis of Presentation and Accounting Policies Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	$ (266)		$ (266)		$ (11,593)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	0		0		75
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	0		0		4
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent			1,994
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Parent			(260)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax, Portion Attributable to Parent			(6)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent			1,728
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest			153
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Noncontrolling Interest			13
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest			(5)
Other Comprehensive Income (Loss), before Tax	430	$ 369	1,889	$ (8,318)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Parent			(698)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Parent			91
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax, Portion Attributable to Parent			2
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent			(605)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Noncontrolling Interest			0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Noncontrolling Interest			0
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax, Portion Attributable to Noncontrolling Interest			0
Other Comprehensive Income (Loss), Tax	151	182	605	(2,612)
Accumulated other comprehensive loss, net of tax	(266)		(266)		(11,514)
Other Comprehensive Income (Loss), Net of Tax	279	$ 187	1,284	$ (5,706)
Non-Controlling Interests In Subsidiaries [Member]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(1,460)		(1,460)		(1,613)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(4)		(4)		(17)
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	$ (2)		(2)		$ 3
Other Comprehensive Income (Loss), Net of Tax			161
SEACOR Marine Holdings Inc. [Member]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent			10,031
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Parent			94
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax, Portion Attributable to Parent			0
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent			$ 10,125