Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In-Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net of Tax [Member]	Class A Common Stock Held By Subsidiaries [Member]	Total Lazard Ltd Stockholders' Equity [Member]	Noncontrolling Interests [Member]
Balance at Dec. 31, 2017	$ 1,258,905	$ 1,298	$ 788,140	$ 1,080,413	$ (232,518)	$ (437,530)	$ 1,199,803	$ 59,102
Balance (in shares) at Dec. 31, 2017		129,766,091				10,747,142
Comprehensive income (loss):
Net income	418,765			413,729			413,729	5,036
Other comprehensive income (loss) - net of tax	(27,846)				(27,847)		(27,847)	1
Amortization of share-based incentive compensation	218,186		218,186				218,186
Dividend equivalents	(5,509)		38,923	(44,432)			(5,509)
Class A common stock dividends	(307,850)			(307,850)			(307,850)
Purchase of Class A common stock	$ (306,591)					$ (306,591)	(306,591)
Purchase of Class A common stock (in shares)	5,797,789					5,797,789
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense (benefit)	$ (117,230)		(345,023)			$ 227,793	(117,230)
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense (benefit) (in shares)						(5,249,819)
Business acquisitions and related equity transactions:
Delivery of Class A common stock			(61)			$ 61
Delivery of Class A common stock (in shares)						(1,858)
Class A common stock issuable (including related amortization)	434		434				434
Dividend equivalents			1,250	(1,250)
Distributions to noncontrolling interests, net	(9,679)							(9,679)
Balance at Sep. 30, 2018	1,121,585	$ 1,298	701,849	1,140,610	(260,365)	$ (516,267)	1,067,125	54,460
Balance (in shares) at Sep. 30, 2018		129,766,091				11,293,254
Balance at Jun. 30, 2018	1,113,104	$ 1,298	652,013	1,092,381	(253,499)	$ (437,031)	1,055,162	57,942
Balance (in shares) at Jun. 30, 2018		129,766,091				9,719,895
Comprehensive income (loss):
Net income	108,725			107,074			107,074	1,651
Other comprehensive income (loss) - net of tax	(6,864)				(6,866)		(6,866)	2
Amortization of share-based incentive compensation	48,356		48,356				48,356
Dividend equivalents	(828)		5,296	(6,124)			(828)
Class A common stock dividends	(52,622)			(52,622)			(52,622)
Purchase of Class A common stock	(82,796)					$ (82,796)	(82,796)
Purchase of Class A common stock (in shares)						1,650,263
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense (benefit)	(500)		(4,060)			$ 3,560	(500)
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense (benefit) (in shares)						(76,904)
Business acquisitions and related equity transactions:
Class A common stock issuable (including related amortization)	145		145				145
Dividend equivalents			99	(99)
Distributions to noncontrolling interests, net	(5,135)							(5,135)
Balance at Sep. 30, 2018	1,121,585	$ 1,298	701,849	1,140,610	(260,365)	$ (516,267)	1,067,125	54,460
Balance (in shares) at Sep. 30, 2018		129,766,091				11,293,254
Balance at Dec. 31, 2018	970,093	$ 1,298	750,692	1,195,563	(273,818)	$ (756,884)	916,851	53,242
Balance (in shares) at Dec. 31, 2018		129,766,091				17,574,805
Comprehensive income (loss):
Net income	218,185			209,523			209,523	8,662
Other comprehensive income (loss) - net of tax	(14,803)				(14,803)		(14,803)
Amortization of share-based incentive compensation	226,272		220,364				220,364	5,908
Dividend equivalents	(6,121)		24,492	(30,613)			(6,121)
Class A common stock dividends	(205,559)			(205,559)			(205,559)
Purchase of Class A common stock	$ (430,281)					$ (430,281)	(430,281)
Purchase of Class A common stock (in shares)	11,946,943					11,946,943
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense (benefit)	$ (92,537)		(330,082)			$ 237,545	(92,537)
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense (benefit) (in shares)						(5,571,166)
Business acquisitions and related equity transactions:
Class A common stock issuable (including related amortization)	16,005		16,005				16,005
Dividend equivalents			532	(532)
Distributions to noncontrolling interests, net	(7,720)							(7,720)
Consolidation of VIEs	12,687							12,687
Balance at Sep. 30, 2019	686,221	$ 1,298	682,003	1,168,382	(288,621)	$ (949,620)	613,442	72,779
Balance (in shares) at Sep. 30, 2019		129,766,091				23,950,582
Balance at Jun. 30, 2019	717,878	$ 1,298	582,342	1,179,901	(271,984)	$ (872,755)	618,802	99,076
Balance (in shares) at Jun. 30, 2019		129,766,091				21,761,253
Comprehensive income (loss):
Net income	48,196			46,704			46,704	1,492
Other comprehensive income (loss) - net of tax	(16,636)				(16,637)		(16,637)	1
Amortization of share-based incentive compensation	65,189		95,162				95,162	(29,973)
Dividend equivalents	(1,440)		4,350	(7,852)			(3,502)	2,062
Class A common stock dividends	(50,235)			(50,235)			(50,235)
Purchase of Class A common stock	(78,569)					$ (78,569)	(78,569)
Purchase of Class A common stock (in shares)						2,231,940
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense (benefit)	(806)		(2,510)			$ 1,704	(806)
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense (benefit) (in shares)						(42,611)
Business acquisitions and related equity transactions:
Class A common stock issuable (including related amortization)	2,523		2,523				2,523
Dividend equivalents			136	(136)
Distributions to noncontrolling interests, net	(1,102)							(1,102)
Consolidation of VIEs	1,223							1,223
Balance at Sep. 30, 2019	$ 686,221	$ 1,298	$ 682,003	$ 1,168,382	$ (288,621)	$ (949,620)	$ 613,442	$ 72,779
Balance (in shares) at Sep. 30, 2019		129,766,091				23,950,582