Cost Saving Initiatives - Schedule of Expenses and Cumulative Expenses Associated With Implementation of Cost Savings Initiatives (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended			3 Months Ended									6 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Compensation and Benefits [Member]	Mar. 31, 2013 Other [Member]	Mar. 31, 2013 Cumulative [Member]	Mar. 31, 2013 Cumulative [Member] Compensation and Benefits [Member]	Mar. 31, 2013 Cumulative [Member] Other [Member]	Mar. 31, 2013 Operating Segments [Member] Financial Advisory [Member]	Mar. 31, 2013 Operating Segments [Member] Financial Advisory [Member] Compensation and Benefits [Member]	Mar. 31, 2013 Operating Segments [Member] Financial Advisory [Member] Other [Member]	Mar. 31, 2013 Operating Segments [Member] Asset Management [Member]	Mar. 31, 2013 Operating Segments [Member] Asset Management [Member] Compensation and Benefits [Member]	Mar. 31, 2013 Operating Segments [Member] Asset Management [Member] Other [Member]	Mar. 31, 2013 Operating Segments [Member] Corporate [Member]	Mar. 31, 2013 Operating Segments [Member] Corporate [Member] Compensation and Benefits [Member]	Mar. 31, 2013 Operating Segments [Member] Corporate [Member] Other [Member]	Mar. 31, 2013 Operating Segments [Member] Cumulative [Member] Financial Advisory [Member]	Mar. 31, 2013 Operating Segments [Member] Cumulative [Member] Financial Advisory [Member] Compensation and Benefits [Member]	Mar. 31, 2013 Operating Segments [Member] Cumulative [Member] Financial Advisory [Member] Other [Member]	Mar. 31, 2013 Operating Segments [Member] Cumulative [Member] Asset Management [Member]	Mar. 31, 2013 Operating Segments [Member] Cumulative [Member] Asset Management [Member] Compensation and Benefits [Member]	Mar. 31, 2013 Operating Segments [Member] Cumulative [Member] Asset Management [Member] Other [Member]	Mar. 31, 2013 Operating Segments [Member] Cumulative [Member] Corporate [Member]	Mar. 31, 2013 Operating Segments [Member] Cumulative [Member] Corporate [Member] Compensation and Benefits [Member]	Mar. 31, 2013 Operating Segments [Member] Cumulative [Member] Corporate [Member] Other [Member]
Restructuring and Related Cost [Abstract]
Cost Saving Initiatives	$ 26,322	$ 24,671	$ 1,651	$ 128,898	$ 124,658	$ 4,240	$ 22,015	$ 20,394	$ 1,621	$ 235	$ 236	$ (1)	$ 4,072	$ 4,041	$ 31	$ 99,547	$ 96,527	$ 3,020	$ 13,024	$ 12,292	$ 732	$ 16,327	$ 15,839	$ 488