Special Purpose Entities, Including Variable Interest Entities - Additional Information (Detail) - Scenario, Unspecified [Domain] $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($) Transactions Entity	Dec. 31, 2014 USD ($) Entity
Variable Interest Entities [Line Items]
Number of VIEs AAC Transferred Assets To	2
Number of VIEs Liquidated	1
Fair value of special purpose entities	$ 9,704	$ 12,036
Asset-Backed Securities and Utility Obligations [Member]
Variable Interest Entities [Line Items]
Weighted average life	6 years 9 months 12 days
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	$ 457,960	$ 457,960
Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number of DeConsolidated Variable Interest Entities	1
Number of consolidated Variable Interest Entities | Entity	14	15
Consolidated VIE assets	$ 15,762,398	$ 15,126,110
Consolidated VIE liabilities	$ 15,674,212	$ 15,085,685
Standard & Poor's, BBB Rating [Member] | Asset-Backed Securities and Utility Obligations [Member]
Variable Interest Entities [Line Items]
Average rating of assets held by sponsored special purpose entities