Schedule I - Condensed Statements of Comprehensive Income (Parent Company Only) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
NET INCOME	$ 402,461	$ 286,500	$ 527,125
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Currency translation adjustments	52,862	9,551	(46,602)
Employee benefit plans:
Prior service costs (net of tax benefit of $17, $17 and $543 for the years ended December 31, 2020, 2019 and 2018, respectively)	(83)	(84)	(2,653)
Actuarial loss (net of tax expense (benefit) of $(1,414), $(9,219) and $131 for the years ended December 31, 2020, 2019 and 2018, respectively)	(3,543)	(34,014)	(2,781)
Adjustments for items reclassified to earnings (net of tax expense of $1,476, $1,167 and $2,335 for the years ended December 31, 2020, 2019 and 2018, respectively)	6,046	4,717	10,735
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	55,282	(19,830)	(41,301)
COMPREHENSIVE INCOME ATTRIBUTABLE TO LAZARD LTD	457,741	266,670	485,825
Parent Company [Member]
NET INCOME	402,461	286,500	527,125
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Currency translation adjustments	52,860	9,551	(46,601)
Employee benefit plans:
Prior service costs (net of tax benefit of $17, $17 and $543 for the years ended December 31, 2020, 2019 and 2018, respectively)	(83)	(84)	(2,653)
Actuarial loss (net of tax expense (benefit) of $(1,414), $(9,219) and $131 for the years ended December 31, 2020, 2019 and 2018, respectively)	(3,543)	(34,014)	(2,781)
Adjustments for items reclassified to earnings (net of tax expense of $1,476, $1,167 and $2,335 for the years ended December 31, 2020, 2019 and 2018, respectively)	6,046	4,717	10,735
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	55,280	(19,830)	(41,300)
COMPREHENSIVE INCOME ATTRIBUTABLE TO LAZARD LTD	$ 457,741	$ 266,670	$ 485,825