Equity-Based Compensation - Narrative (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units expected to vest	167,000
Compensation expense expected to vest period	6 years 9 months 4 days
Options Granted	0
Unamortized compensation cost related to unvested share options	$ 500,000
Weighted average period	4 years 3 months 18 days
Class Shares In Settlement Of Vested Rsus And Exercised Share Options	2,671,869
Ownership interest maximum	39.40%
Ownership interest minimum	39.00%
AOG unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of the AOG units to compensation expense	5,600,000,000
Minimum compensation service expense period	5 years
Maximum compensation service expense period	6 years
Compensation expense		15,000,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	30,600,000	27,500,000
Number of units expected to vest	7,700,000
Compensation expense expected to vest period	3 years 2 months 12 days
Actual forfeiture rate	8.00%	0.90%
Equity Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	28,100,000	1,200,000
AAA Restricted Depositary Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	200,000	300,000
Employee awards vesting period	3 years
Number of units expected to vest	120,354	114,896
Actual forfeiture rate	1.00%	1.00%
Accrued compensation liability	1,200,000	1,000,000
Additional paid in capital decreased	2,500,000	1,400,000
Liability for undelivered RDUs	200,000	1,200,000
Restricted Depository Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units expected to vest	245,000
Compensation expense expected to vest period	3 years
Options Granted	0
ARI Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	300,000	1,000,000
Actual forfeiture rate	0.00%	0.00%
Management fees	300,000	1,400,000
AMTG Restricted Stock Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	200,000	300,000
Employee awards vesting period	3 years
Compensation expense expected to vest period	1 year 9 months 18 days
Actual forfeiture rate	0.00%	0.00%
Management fees	$ 300,000	$ 300,000
Shares expected to vest	117,000
Ari Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense expected to vest period	1 year 8 months 12 days
Shares expected to vest	166,000
2007 Omnibus Equity Incentive Plan, Plan Grants | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Unit, Fair Value Price, Marketability Discount, No Distributions	35.20%	15.30%
Restricted Stock Unit, Fair Value Price, Marketability Discount	5.00%	5.00%
Employee awards vesting period	6 years
2007 Omnibus Equity Incentive Plan, Bonus Grants | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Unit, Fair Value Price, Marketability Discount	3.00%	5.00%
Employee awards vesting period	3 years