Gains and losses (realized and unrealized) included in earnings for level 3 assets and liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	$ (1,847)	$ (8,249)	$ (6,780)	$ (16,610)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	3,671	(1,206)	7,835	(38)
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	2,695	(3,254)	2,052	(6,445)
Fair Value Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss	3,671	(1,206)	7,835	(38)
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings	1,824	(9,455)	1,055	(16,648)
Fair Value Assets And Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss Total	6,366	(4,460)	9,887	(6,483)
Interest Income Member
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	(1)	0	(3)
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	0	0	0	0
Mortgage Banking Activities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(1,917)	(7,740)	(6,846)	(15,836)
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	2,570	(2,818)	1,886	(5,842)
Trading Gains Losses [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	70	(508)	66	(771)
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	125	(436)	166	(603)
F D I C Loss Share Expense Income [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	3,671	(1,206)	7,835	(38)
Fair Value Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss	$ 3,671	$ (1,206)	$ 7,835	$ (38)