Note Allowance for loan losses (Troubled debt restructuring according to their accruing status) (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	$ 124,037		$ 140,438
Commercial
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	55,098		71,419
Construction
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	172		158
Mortgages
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	43,252		42,570
Leasing
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	608		687
Consumer
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	24,907		$ 25,604
Non Covered Loans
Troubled Debt Restructuring
Troubled debt restructurings	1,179,908	$ 1,151,343
Non Covered Loans | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	116,510	106,184
Non Covered Loans | Commercial
Troubled Debt Restructuring
Troubled debt restructurings	258,375	254,532
Non Covered Loans | Commercial | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	47,571	37,355
Non Covered Loans | Construction
Troubled Debt Restructuring
Troubled debt restructurings	2,020	2,480
Non Covered Loans | Construction | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	172	264
Non Covered Loans | Mortgages
Troubled Debt Restructuring
Troubled debt restructurings	800,413	774,496
Non Covered Loans | Mortgages | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	43,252	44,029
Non Covered Loans | Leasing
Troubled Debt Restructuring
Troubled debt restructurings	2,391	2,400
Non Covered Loans | Leasing | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	608	573
Non Covered Loans | Consumer
Troubled Debt Restructuring
Troubled debt restructurings	116,709	117,435
Non Covered Loans | Consumer | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	24,907	23,963
Covered loans
Troubled Debt Restructuring
Troubled debt restructurings	5,458	6,596
Covered loans | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0	0
Covered loans | Mortgages
Troubled Debt Restructuring
Troubled debt restructurings	5,458	6,596
Covered loans | Mortgages | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0	0
Non-Accruing | Non Covered Loans
Troubled Debt Restructuring
Troubled debt restructurings	223,579	234,273
Non-Accruing | Non Covered Loans | Commercial
Troubled Debt Restructuring
Troubled debt restructurings	87,841	88,117
Non-Accruing | Non Covered Loans | Construction
Troubled Debt Restructuring
Troubled debt restructurings	1,826	2,259
Non-Accruing | Non Covered Loans | Mortgages
Troubled Debt Restructuring
Troubled debt restructurings	120,694	130,483
Non-Accruing | Non Covered Loans | Leasing
Troubled Debt Restructuring
Troubled debt restructurings	642	609
Non-Accruing | Non Covered Loans | Consumer
Troubled Debt Restructuring
Troubled debt restructurings	12,576	12,805
Non-Accruing | Covered loans
Troubled Debt Restructuring
Troubled debt restructurings	2,500	3,268
Non-Accruing | Covered loans | Mortgages
Troubled Debt Restructuring
Troubled debt restructurings	2,500	3,268
Accruing | Non Covered Loans
Troubled Debt Restructuring
Troubled debt restructurings	956,329	917,070
Accruing | Non Covered Loans | Commercial
Troubled Debt Restructuring
Troubled debt restructurings	170,534	166,415
Accruing | Non Covered Loans | Construction
Troubled Debt Restructuring
Troubled debt restructurings	194	221
Accruing | Non Covered Loans | Mortgages
Troubled Debt Restructuring
Troubled debt restructurings	679,719	644,013
Accruing | Non Covered Loans | Leasing
Troubled Debt Restructuring
Troubled debt restructurings	1,749	1,791
Accruing | Non Covered Loans | Consumer
Troubled Debt Restructuring
Troubled debt restructurings	104,133	104,630
Accruing | Covered loans
Troubled Debt Restructuring
Troubled debt restructurings	2,958	3,328
Accruing | Covered loans | Mortgages
Troubled Debt Restructuring
Troubled debt restructurings	$ 2,958	$ 3,328