Interim Financial Statements - Additional Information (Detail) - GulfMark	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Interim Financial Statements [Line Items]
Business acquisition, name of acquired entity	GulfMark Offshore, Inc.	GulfMark Offshore, Inc.
Business acquisition, effective date of acquisition	Nov. 15, 2018	Nov. 15, 2018
Business acquisition, date of acquisition agreement	Jul. 15, 2018	Jul. 15, 2018