Goodwill and Other Intangible Assets - Estimated Future Amortization Expense (Parenthetical) (Detail)	12 Months Ended
Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Percentage of intangible asset amortization attributable to non-controlling interests	35.00%

Percentage of intangible asset amortization attributable to non-controlling interests.

No definition available.

Name:	laz_PercentageOfIntangibleAssetAmortizationAttributableToNoncontrollingInterests
Namespace Prefix:	laz_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration