Note Allowance for loan losses (Troubled debt restructuring according to their accruing status) (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	$ 118,072		$ 124,037
Commercial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	51,276		55,098
Construction
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		172
Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	43,264		43,252
Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	522		608
Consumer
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	23,010		$ 24,907
Non Covered Loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	1,255,355	$ 1,246,577
Non Covered Loans | TDR
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	112,123	109,812
Non Covered Loans | Commercial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	250,809	260,044
Non Covered Loans | Commercial | TDR
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	45,327	40,810
Non Covered Loans | Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	891,740	871,997
Non Covered Loans | Mortgages | TDR
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	43,264	44,610
Non Covered Loans | Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	1,804	1,817
Non Covered Loans | Leasing | TDR
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	522	535
Non Covered Loans | Consumer
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	111,002	112,719
Non Covered Loans | Consumer | TDR
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	23,010	23,857
Covered loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	5,758	5,530
Covered loans | TDR
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0	0
Covered loans | Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	5,758	5,530
Covered loans | Mortgages | TDR
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0	0
Non-Accruing | Non Covered Loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	222,811	223,104
Non-Accruing | Non Covered Loans | Commercial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	79,571	83,157
Non-Accruing | Non Covered Loans | Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	130,589	127,071
Non-Accruing | Non Covered Loans | Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	230	434
Non-Accruing | Non Covered Loans | Consumer
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	12,421	12,442
Non-Accruing | Covered loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	2,804	2,580
Non-Accruing | Covered loans | Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	2,804	2,580
Accruing | Non Covered Loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	1,032,544	1,023,473
Accruing | Non Covered Loans | Commercial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	171,238	176,887
Accruing | Non Covered Loans | Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	761,151	744,926
Accruing | Non Covered Loans | Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	1,574	1,383
Accruing | Non Covered Loans | Consumer
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	98,581	100,277
Accruing | Covered loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	2,954	2,950
Accruing | Covered loans | Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Troubled debt restructurings	$ 2,954	$ 2,950