Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Parenthetical) (Detail) - Scenario, Unspecified [Domain] - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Notional outstanding	$ 1,447,939	$ 1,529,759
Other Contracts [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Notional outstanding	$ 58,482	$ 58,800
Weighted average life (WAL) in years	8 months	1 year 2 months 12 days
Weighted average quotes	0.00%	1.00%
CVA percentage	2.25%	2.21%
Weighted average credit rating	A+	A
Fair value of derivative liabilities	$ 36	$ 328