Incentive Plans - Schedule of Activity Relating to RSUs and DSUs (Parenthetical) (Detail) - shares	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Dividend participation rights	406,886	535,695

Issuance of restricted stock units in connection with dividend participation rights.

No definition available.

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Namespace Prefix:	laz_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration