Note Fair value measurement (Assets measured at fair value on nonrecurring basis) (Detail) - Fair Value, Measurements, Nonrecurring - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Fair Value by Asset Class [Domain]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	[1]	$ 29,826	$ 45,133
Other real estate owned	[2]	14,397	17,155
Other Foreclosed Assets	[2]	2,045	165
Total		46,268	62,453
Write-down		(17,405)	(21,142)
Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write-down	[1]	(13,766)	(16,491)
Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write-down	[2]	(3,116)	(4,578)
Other foreclosed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write-down	[2]	(523)	(73)
Level 1 | Fair Value by Asset Class [Domain]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	[1]	0	0
Other real estate owned	[2]	0	0
Other Foreclosed Assets	[2]	0	0
Total		0	0
Level 2 | Fair Value by Asset Class [Domain]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	[1]	0	0
Other real estate owned	[2]	0	0
Other Foreclosed Assets	[2]	0	0
Total		0	0
Level 3 | Fair Value by Asset Class [Domain]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	[1]	29,826	45,133
Other real estate owned	[2]	14,397	17,155
Other Foreclosed Assets	[2]	2,045	165
Total		$ 46,268	$ 62,453

[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 . Costs to sell are excluded from the reported fair value amount .

[2] Represents the fair value of foreclosed real estate and other collateral owned that were written d own to their fair value. Costs to sell are excluded from the reported fair value amount.