Gains and losses (realized and unrealized) included in earnings for level 3 assets and liabilities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
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	$ (2,537)	$ 3,887	$ (19,147)	$ (7,228)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	1,078	(5,322)	1,040	(12,573)
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	2,633	9,478	(3,813)	13,442
Fair Value Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss	1,078	(5,322)	1,040	(12,573)
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings	(1,459)	(1,435)	(18,107)	(19,801)
Fair Value Assets And Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss Total	3,711	4,156	(2,773)	869
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	(1)	(2)	(4)	(5)
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	(2,588)	3,879	(18,424)	(6,862)
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	2,528	9,342	(3,314)	13,355
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	52	10	(719)	(361)
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	105	136	(499)	87
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	1,078	(5,322)	1,040	(12,573)
Fair Value Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss	$ 1,078	$ (5,322)	$ 1,040	$ (12,573)