Stockholders' Equity - Accumulated Other Comprehensive Income (Loss), Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			$ 1,293,813	$ 1,367,306
Other comprehensive income (loss) before reclassifications	$ 17,558	$ (16,579)	33,995	(4,981)
Adjustments for items reclassified to earnings, net of tax	1,356	1,121	2,442	2,307
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	18,914	(15,458)	36,437	(2,674)
Balance	1,302,713	1,204,344	1,302,713	1,204,344
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(138,272)	(85,545)	(155,204)	(97,284)
Other comprehensive income (loss) before reclassifications	26,167	(16,104)	43,099	(4,365)
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	26,167	(16,104)	43,099	(4,365)
Balance	(112,105)	(101,649)	(112,105)	(101,649)
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(158,429)	(136,028)	(159,020)	(137,073)
Other comprehensive income (loss) before reclassifications	(8,609)	(475)	(9,104)	(616)
Adjustments for items reclassified to earnings, net of tax	1,356	1,121	2,442	2,307
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(7,253)	646	(6,662)	1,691
Balance	(165,682)	(135,382)	(165,682)	(135,382)
Total AOCI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(296,701)	(221,573)	(314,224)	(234,357)
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	18,914	(15,458)	36,437	(2,674)
Balance	(277,787)	(237,031)	(277,787)	(237,031)
AOCI Attributable to Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(2)	(1)	(2)	(1)
Balance	(2)	(1)	(2)	(1)
Total Lazard LTD AOCI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(296,699)	(221,572)	(314,222)	(234,356)
Other comprehensive income (loss) before reclassifications	17,558	(16,579)	33,995	(4,981)
Adjustments for items reclassified to earnings, net of tax	1,356	1,121	2,442	2,307
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	18,914	(15,458)	36,437	(2,674)
Balance	$ (277,785)	$ (237,030)	$ (277,785)	$ (237,030)