Assets measured at fair value on nonrecurring basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2013 Fair Value, Measurements, Nonrecurring [Member]		Jun. 30, 2012 Fair Value, Measurements, Nonrecurring [Member]		Jun. 30, 2013 Fair Value, Measurements, Nonrecurring [Member] Fair Value, Inputs, Level 1 [Member]		Jun. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Fair Value, Inputs, Level 1 [Member]		Jun. 30, 2013 Fair Value, Measurements, Nonrecurring [Member] Fair Value, Inputs, Level 2 [Member]		Jun. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Fair Value, Inputs, Level 2 [Member]		Jun. 30, 2013 Fair Value, Measurements, Nonrecurring [Member] Fair Value, Inputs, Level 3 [Member]		Jun. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Fair Value, Inputs, Level 3 [Member]		Jun. 30, 2013 Fair Value, Measurements, Nonrecurring [Member] Unrealized Gain (Loss or Write-down) [Member]		Jun. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Unrealized Gain (Loss or Write-down) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans							$ 40,801	[1]	$ 24,151	[1]	$ 0	[1]	$ 0	[1]	$ 0	[1]	$ 0	[1]	$ 40,801	[1]	$ 24,151	[1]	$ (22,048)	[1]	$ (2,769)	[1]
Loans held-for-sale	0	0	8,813	4,779	186,488	376,582	0	[2]	177,460	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	177,460	[2]	(364,820)	[2]	(38,244)	[2]
Other real estate owned							59,193	[3]	87,185	[4]	0	[3]	0	[4]	14,788	[3]	5,944	[4]	44,405	[3]	81,241	[4]	(22,164)	[3]	(22,748)	[4]
Other Repossessed Assets							230	[3]	144	[4]	0	[3]	0	[4]	0	[3]	0	[4]	230	[3]	144	[4]	(69)	[3]	(208)	[4]
Assets Held-for-sale, Long Lived							0		1,100	[5]	0		0	[5]	0		0	[5]	0		1,100	[5]	0		(123)	[5]
Total							$ 100,224		$ 290,040		$ 0		$ 0		$ 14,788		$ 5,944		$ 85,436		$ 284,096		$ (409,101)		$ (64,092)

[1] Relates mostly to certain impaired collateral dependent loans. The impairment was measured based on the fair value of the collateral, which is derived from appraisals that take into consideration prices in observed transactions involving similar assets in similar locations, in accordance with the provisions of ASC Section 310-10-35.

[2] Relates to lower of cost or fair value adjustments on loans held-for-sale and loans transferred from loans held-in-portfolio to loans held-for-sale.

[3] Represents the fair value of foreclosed real estate and other collateral owned that were written down to their fair value. Costs to sell excluded from the reported fair value amount were $3 million at June 30, 2013.

[4] Represents the fair value of foreclosed real estate and other collateral owned that were written down to their fair value. Costs to sell excluded from the reported fair value amount were $5 million at June 30, 2012.

[5] Represents the fair value of long-lived assets held-for-sale that were written down to their fair value.