Schedule I - Condensed Statements of Comprehensive Income (Parent Company Only) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
NET INCOME	$ 113,396	$ 107,074	$ 146,963	$ 159,692	$ (83,558)	$ 109,210	$ 120,378	$ 107,553	$ 527,125	$ 253,583	$ 387,698
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Currency translation adjustments									(46,602)	71,669	(57,920)
Employee benefit plans:
Prior service costs (net of tax benefit of $543 for the year ended December 31, 2018)									(2,653)
Actuarial gain (loss) (net of tax expense (benefit) of $131, $(3,507) and $(5,205) for the years ended December 31, 2018, 2017 and 2016, respectively)									(2,781)	2,085	(24,473)
Adjustments for items reclassified to earnings (net of tax expense of $2,335, $2,220 and $1,757 for the years ended December 31, 2018, 2017 and 2016, respectively)									10,735	7,951	2,526
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX									(41,301)	81,705	(79,867)
COMPREHENSIVE INCOME ATTRIBUTABLE TO LAZARD LTD									485,825	335,287	307,832
Parent Company [Member]
NET INCOME									527,125	253,583	387,698
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Currency translation adjustments									(46,601)	71,668	(57,919)
Employee benefit plans:
Prior service costs (net of tax benefit of $543 for the year ended December 31, 2018)									(2,653)
Actuarial gain (loss) (net of tax expense (benefit) of $131, $(3,507) and $(5,205) for the years ended December 31, 2018, 2017 and 2016, respectively)									(2,781)	2,085	(24,473)
Adjustments for items reclassified to earnings (net of tax expense of $2,335, $2,220 and $1,757 for the years ended December 31, 2018, 2017 and 2016, respectively)									10,735	7,951	2,526
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX									(41,300)	81,704	(79,866)
COMPREHENSIVE INCOME ATTRIBUTABLE TO LAZARD LTD									$ 485,825	$ 335,287	$ 307,832