Related Party Transactions - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended		12 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended	9 Months Ended	12 Months Ended		1 Months Ended	3 Months Ended		9 Months Ended				1 Months Ended	3 Months Ended		9 Months Ended				3 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended			12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended						3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Aug. 31, 2013	May 04, 2012	Jun. 28, 2013 NASDAQ OMX [Member]	Sep. 30, 2013 Cantor and ELX [Member]	Sep. 30, 2012 Cantor and ELX [Member]	Sep. 30, 2013 Cantor and ELX [Member]	Sep. 30, 2012 Cantor and ELX [Member]	Sep. 30, 2013 Cantor [Member]	Sep. 30, 2013 Cantor [Member]	Dec. 31, 2012 Cantor [Member]	Sep. 30, 2013 Class A Common Stock [Member]	Sep. 30, 2012 Class A Common Stock [Member]	Sep. 30, 2013 Class A Common Stock [Member]	Sep. 30, 2012 Class A Common Stock [Member]	Dec. 31, 2012 Class A Common Stock [Member]	Sep. 30, 2013 ELX [Member]	Dec. 31, 2012 ELX [Member]	Mar. 28, 2012 ELX [Member]	Jun. 26, 2013 8.125% Senior Notes [Member]	Sep. 30, 2013 8.125% Senior Notes [Member]	Sep. 30, 2012 8.125% Senior Notes [Member]	Sep. 30, 2013 8.125% Senior Notes [Member]	Sep. 30, 2012 8.125% Senior Notes [Member]	Dec. 31, 2012 8.125% Senior Notes [Member]	Jun. 26, 2012 8.125% Senior Notes [Member]	Apr. 30, 2010 8.75% Convertible Notes [Member]	Sep. 30, 2013 8.75% Convertible Notes [Member]	Sep. 30, 2012 8.75% Convertible Notes [Member]	Sep. 30, 2013 8.75% Convertible Notes [Member]	Sep. 30, 2012 8.75% Convertible Notes [Member]	Dec. 31, 2012 8.75% Convertible Notes [Member]	Apr. 01, 2010 8.75% Convertible Notes [Member]	Jun. 30, 2013 Global Partnership Restructuring Program [Member]	Sep. 30, 2013 Global Partnership Restructuring Program [Member]	Sep. 30, 2013 Grubb & Ellis Company [Member]	Apr. 13, 2012 Grubb & Ellis Company [Member]	Sep. 30, 2013 Service Agreements [Member]	Sep. 30, 2012 Service Agreements [Member]	Sep. 30, 2013 Service Agreements [Member]	Sep. 30, 2012 Service Agreements [Member]	Sep. 30, 2013 Stephen M. Merkel [Member] Class A Common Stock [Member]	Dec. 31, 2012 Stephen M. Merkel [Member] Class A Common Stock [Member]	Sep. 30, 2013 Charity Day [Member] Class A Common Stock [Member]	Dec. 31, 2012 Charity Day [Member] Class A Common Stock [Member]	Sep. 30, 2013 Aqua [Member]	Sep. 30, 2012 Aqua [Member]	Aug. 05, 2013 Aqua [Member]	Sep. 30, 2013 Aqua [Member] Cantor [Member]	Sep. 30, 2013 Cantor and Freedom International Brokerage [Member]	Dec. 31, 2012 Cantor and Freedom International Brokerage [Member]	Sep. 30, 2013 Employee Loans [Member]	Sep. 30, 2012 Employee Loans [Member]	Sep. 30, 2013 Employee Loans [Member]	Sep. 30, 2012 Employee Loans [Member]	Dec. 31, 2012 Employee Loans [Member]	Sep. 30, 2013 Controlled Equity Offerings [Member]	Sep. 30, 2012 Controlled Equity Offerings [Member]	Sep. 30, 2013 Controlled Equity Offerings [Member]	Sep. 30, 2012 Controlled Equity Offerings [Member]	Dec. 31, 2012 Cantor Rights to Purchase Exchangeable Units [Member]	Jun. 30, 2013 Executive Officers [Member]	Sep. 30, 2013 Executive Officers [Member] Class A Common Stock [Member]	Jun. 30, 2013 Executive Officers [Member] Global Partnership Restructuring Program [Member]	Jun. 30, 2013 Executive Officers [Member] Global Partnership Restructuring Program [Member] Class A Common Stock [Member]	Sep. 30, 2013 Shaun D. Lynn [Member] Class A Common Stock [Member]
Related Party Transaction [Abstract]
Mark-up cost of services																																													7.50%
Company ownership of Tower Bridge																																													52.00%
Cantor ownership of Tower Bridge																																											48.00%		48.00%
Equity investment in ELX				$ 1,171,000	$ 17,205,000																	$ 0	$ 16,000,000																												$ 1,200,000	$ 1,200,000
Credit agreement commitment to variable interest entity																						16,000,000		16,000,000
Credit facility commitment period																						Mar. 28, 2015
Amount Loaned under credit agreement to ELX																						0
Recognized related party revenues	8,071,000		13,102,000	33,461,000	39,143,000					8,100,000	13,100,000	33,500,000	39,100,000
Service charges																																											8,200,000	9,400,000	24,900,000	26,500,000
Compensation to leased employees																																											6,100,000	6,600,000	17,700,000	17,000,000
Cantor's share of net profit in Tower Bridge																																											600,000	1,000,000	700,000	1,400,000
Interest income related to Reverse Repurchase Agreements														68,000	68,000
Investment in asset-backed commercial paper program	200,000,000			200,000,000
Investment authorization in asset-backed commercial paper program							350,000,000
Receivables from Cantor and Freedom International Brokerage																																																							4,200,000	2,900,000
Employee loans	127,390,000			127,390,000		220,098,000																																																			127,400,000		127,400,000		220,100,000
Compensation expense related to employee loans																																																									7,700,000	9,000,000	187,900,000	24,100,000
Recognized reserve		160,500,000
Principal amount of notes																															112,500,000		150,000,000		150,000,000		150,000,000	150,000,000
Repayment of Senior Notes																																150,000,000
Debt instrument maturity year																									2042										2015
Convertible notes issuance date																																			Apr. 01, 2010
Interest expense related to the 8.75% Convertible Notes	2,900,000		2,900,000																							2,300,000	2,300,000	6,900,000	2,400,000				3,300,000	3,300,000	9,800,000	9,800,000
Stated interest rate																									8.125%	8.125%		8.125%		8.125%			8.75%		8.75%		8.75%	8.75%
Related party expenses related to the Company's controlled equity offerings																																																														100,000	500,000	700,000	1,400,000
Advisory fee																																										1,000,000
Date of acquisition																																									Apr. 13, 2012
Debt issuance costs																									200,000			3,800,000
Fees paid related to divestiture	7,400,000			7,400,000					7,400,000
Number of non-exchangeable founding/working partner units redeemed				1,802,608																																																														431,985
Consideration for non-exchangeable founding partner units redeemed																																																																		1,282,045
Founding/working partner units remaining for which Cantor has the right to purchase Cantor units																																																																		488,744
Limited partnership units purchased																																																																		431,985
Aggregate consideration paid in connection with the grant of exchangeability and exchange of founding partner units																1,449,663
Limited partnership units Exchange ratio						1
Exchangeable Founding/Working Partner Units						488,744
Non-exchangeable founding/working partner units remaining	2,448,301			2,448,301
Number of partnership units issued to executive officer								2,449,312
Class A common stock repurchased from executive officers																																															33,478	41,523																				999,722			533,406
Average price per share of common stock repurchased from executive officers																																																																				$ 5.77
Average price per share of common stock repurchased				$ 5.77													$ 5.77		$ 5.77	$ 7.66	$ 7.66
Repurchase of Class A common stock				999,722													966,244		999,722	44,013	44,013
Redemption/exchange of limited partnership units																																							77,000,000	77,000,000
Common stock																			2,453,473		4,797,177																		45,000,000																															3,553,345
Common stock issued, restricted shares																																							39,000,000	39,000,000																													3,561,392
Shares withheld for taxes																																																																			1,917,094
Percentage of non-exchangeable units redeemed				9.75%
Shares issued and donated to Relief Fund by company																																																	1,000,000	2,860,000
Charitable contributions				25,000,000
Authorization amount for loans and investments																																																			10,000,000
Increase in loans, investments or other credit support arrangements																																																					1,600,000
Ownership percentage																																																			49.00%			51.00%
Principal sum of loan due from related parties	$ 1,255,000			$ 1,255,000		$ 21,655,000																																													$ 980,000
Maturity date of subordinated loan																																																			Sep. 01, 2015
Loan Receivable, Description of Variable Rate Basis																																																			Three month LIBOR plus 600 basis points
Loan Receivable, Basis Spread on Variable Rate																																																			6.00%