Stockholders' Equity - Changes in Ownership Interests (Detail)	Sep. 30, 2014	Sep. 30, 2013
Lazard Ltd [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Ending balance (in shares)	129,766,090	129,056,081
Percentage of Ownership, Ending Balance	100.00%	99.50%
LAZ-MD Holdings [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Ending balance (in shares)		710,009
Percentage of Ownership, Ending Balance		0.50%
Total Lazard Group Common Membership Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Ending balance (in shares)	129,766,090	129,766,090