Special Purpose Entities, Including Variable Interest Entities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2016 USD ($) Transactions Entity	Dec. 31, 2015 USD ($) Entity
Variable Interest Entities [Line Items]
Equity Method Investments	$ 26,471,000
Number of RMBS Sold	17
Cash Received From Delaware Trust	$ 146,000,000
Number of VIEs AAC Transferred Assets To	2
Number of VIEs Liquidated	1
Secured Debt	$ 122,058,000
Par Value of Securities Placed in Trust	367,986,000
Fair Value of Securities Placed in Trust	381,249,000	$ 396,100,000
Securities Issued by Delaware Trust	146,000,000
Fair value of special purpose entities	8,411,000	8,696,000
Consolidated VIE assets	14,150,874,000	14,288,497,000
Consolidated VIE liabilities	$ 14,077,034,000	14,259,776,000
Asset-Backed Securities and Utility Obligations [Member]
Variable Interest Entities [Line Items]
Weighted average life	5 years 10 months 15 days
Average rating of assets held by sponsored special purpose entities	BBB
Sponsored Variable Interest Entities [Member]
Variable Interest Entities [Line Items]
Number of individual transactions with special purpose entities | Transactions	15
Number of transactions outstanding with special purpose entities | Transactions	3
Total principal amount of debt outstanding	$ 454,510,000	$ 465,160,000
Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number of DeConsolidated Variable Interest Entities	1
Number of consolidated Variable Interest Entities | Entity	15	15
variable interest entities deconsolidation gain loss	$ 0
London Interbank Offered Rate (LIBOR) [Member]
Variable Interest Entities [Line Items]
Interest Rate on Securities Issued by Delaware Trust	2.80%