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, 2016	$ 1,293,813	$ 1,298	$ 688,231	$ 1,134,186	$ (314,222)	$ (273,506)	$ 1,235,987	$ 57,826
Balance (in shares) at Dec. 31, 2016		129,766,091				7,628,786
Adjustment for the cumulative effect on prior years from the adoption of new accounting guidance related to share-based incentive compensation at Dec. 31, 2016	81,544			81,544			81,544
Balance, as adjusted at Dec. 31, 2016	1,375,357	$ 1,298	688,231	1,215,730	(314,222)	$ (273,506)	1,317,531	57,826
Comprehensive income (loss)
Net income	342,801			337,141			337,141	5,660
Other comprehensive income (loss) - net of tax	52,551				52,549		52,549	2
Amortization of share-based incentive compensation	220,648		220,648				220,648
Dividend equivalents	(4,997)		36,482	(41,479)			(4,997)
Class A common stock dividends	(292,293)			(292,293)			(292,293)
Purchase of Class A common stock	$ (252,538)					$ (252,538)	(252,538)
Purchase of Class A common stock (in shares)	5,838,520					5,838,520
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense	$ (72,203)		(212,271)			$ 140,068	(72,203)
Delivery of Class A common stock in connection with share-based incentive compensation and related tax expense (in shares)						(3,772,169)
Business acquisitions and related equity transactions:
Delivery of Class A common stock and related tax benefit	1,437		(472)			$ 1,909	1,437
Delivery of Class A common stock and related tax benefit (in shares)						(47,474)
Class A common stock issuable (including related amortization)	363		363				363
Distributions to noncontrolling interests, net	(3,059)							(3,059)
Other	408			204			204	204
Balance at Sep. 30, 2017	1,368,475	$ 1,298	732,981	1,219,303	(261,673)	$ (384,067)	1,307,842	60,633
Balance (in shares) at Sep. 30, 2017		129,766,091				9,647,663
Balance at Jun. 30, 2017					(277,785)
Comprehensive income (loss)
Net income	111,470
Other comprehensive income (loss) - net of tax	16,114				16,112
Balance at Sep. 30, 2017	1,368,475	$ 1,298	732,981	1,219,303	(261,673)	$ (384,067)	1,307,842	60,633
Balance (in shares) at Sep. 30, 2017		129,766,091				9,647,663
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	$ (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 (in shares)						(5,249,819)
Business acquisitions and related equity transactions:
Delivery of Class A common stock and related tax benefit			(61)			$ 61
Delivery of Class A common stock and related tax benefit (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					(253,499)
Comprehensive income (loss)
Net income	108,725
Other comprehensive income (loss) - net of tax	(6,864)				(6,866)
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