Condensed Consolidated Statements Of Income (Loss) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Operating Revenues	$ 158,171,000	$ 109,570,000	$ 392,376,000	$ 314,269,000
Costs and Expenses [Abstract]
Operating	107,258,000	66,573,000	252,156,000	193,636,000
Administrative and general	20,531,000	20,931,000	68,949,000	64,968,000
Depreciation and amortization	20,501,000	15,864,000	54,689,000	46,005,000
Total costs and expenses	148,290,000	103,368,000	375,794,000	304,609,000
Gains (Losses) on Asset Dispositions and Impairments, Net	5,209,000	(593,000)	10,918,000	2,590,000
Operating Income	15,090,000	5,609,000	27,500,000	12,250,000
Other Income (Expense):
Interest income	2,367,000	4,492,000	6,651,000	13,100,000
Interest expense	9,121,000	9,955,000	31,101,000	29,892,000
Debt extinguishment gains (losses), net	3,000	557,000	(94,000)	5,395,000
Marketable security losses, net	(12,478,000)	(9,484,000)	(13,316,000)	(52,454,000)
Derivative gains (losses), net	0	(862,000)	19,727,000	(3,527,000)
Foreign currency gains, net	969,000	418,000	898,000	2,812,000
Other, net	64,000	(5,461,000)	68,000	(13,110,000)
Total Other Nonoperating Income (Expense)	(18,196,000)	(20,295,000)	(17,167,000)	(77,676,000)
Income (Loss) from Continuing Operations Before Income Tax Benefit and Equity in Earnings (Losses) of 50% or Less Owned Companies	(3,106,000)	(14,686,000)	10,333,000	(65,426,000)
Income Tax Benefit	(12,795,000)	(7,164,000)	(12,563,000)	(29,921,000)
Income (Loss) from Continuing Operations Before Equity in Earnings (Losses) of 50% or Less Owned Companies	9,689,000	(7,522,000)	22,896,000	(35,505,000)
Equity in Earnings (Losses) of 50% or Less Owned Companies, Net of Tax	488,000	(1,112,000)	2,929,000	(7,169,000)
Income (Loss) from Continuing Operations	10,177,000	(8,634,000)	25,825,000	(42,674,000)
Income (Loss) from Discontinued Operations, Net of Tax	10,927,000	(25,392,000)	(23,150,000)	(62,809,000)
Net Income (Loss)	21,104,000	(34,026,000)	2,675,000	(105,483,000)
Net Income Attributable to Noncontrolling Interests in Subsidiaries	3,543,000	5,777,000	13,839,000	16,665,000
Net Income (Loss) attributable to SEACOR Holdings Inc.	$ 17,561,000	$ (39,803,000)	$ (11,164,000)	$ (122,148,000)
Basic Earnings (Loss) Per Common Share of SEACOR Holdings Inc.:
Continuing operations	$ 0.38	$ (0.82)	$ 0.55	$ (3.45)
Discontinued operations	0.62	(1.53)	(1.20)	(3.78)
Basic Earnings (Loss) Per Common Share of SEACOR Holdings Inc.	1.00	(2.35)	(0.65)	(7.23)
Diluted Earnings (Loss) Per Common Share of SEACOR Holdings Inc.:
Continuing operations	0.38	(0.82)	0.55	(3.45)
Discontinued operations	0.62	(1.53)	(1.19)	(3.78)
Diluted Earnings (Loss) Per Common Share of SEACOR Holdings Inc.	$ 1.00	$ (2.35)	$ (0.64)	$ (7.23)
Weighted Average Common Shares Outstanding:
Basic	17,508,770	16,943,647	17,265,140	16,896,751
Diluted	17,637,824	16,943,647	17,510,560	16,896,751