Schedule of Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	4 Months Ended	5 Months Ended	12 Months Ended
	Jul. 31, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Unrecognized Tax Benefits [Line Items]
Begining Balance	$ 400,818	$ 402,868	$ 399,292	$ 404,571
Additions based on tax positions related to the current year	2,050	170	14,741
Additions based on tax positions related to a prior year		2,578	1,964	6,903
Settlement and lapse of statute of limitations		(1,045)	(1,897)	(2,953)
Reductions based on tax positions related to a prior year			(58)	(18,086)
Ending Balance	$ 402,868	$ 404,571	$ 414,042	399,292
GulfMark
Schedule Of Unrecognized Tax Benefits [Line Items]
Additions from GulfMark business combination				$ 8,857