Note Allowance for loan losses (Troubled debt restructuring according to their accruing status) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	$ 101,958		$ 117,015
Commercial
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	33,476		45,028
Construction
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	19		474
Mortgages
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	43,139		46,915
Leasing
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	321		448
Consumer
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	25,003		$ 24,150
Non Covered Loans
Troubled Debt Restructuring
Troubled debt restructurings	1,530,015	$ 1,515,889
Non Covered Loans | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	96,021	112,999
Non Covered Loans | Commercial
Troubled Debt Restructuring
Troubled debt restructurings	345,019	360,679
Non Covered Loans | Commercial | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	29,274	46,889
Non Covered Loans | Construction
Troubled Debt Restructuring
Troubled debt restructurings	1,788	1,788
Non Covered Loans | Construction | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	19	56
Non Covered Loans | Mortgages
Troubled Debt Restructuring
Troubled debt restructurings	1,074,502	1,042,470
Non Covered Loans | Mortgages | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	41,913	41,211
Non Covered Loans | Leasing
Troubled Debt Restructuring
Troubled debt restructurings	1,018	1,108
Non Covered Loans | Leasing | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	321	320
Non Covered Loans | Consumer
Troubled Debt Restructuring
Troubled debt restructurings	107,688	109,844
Non Covered Loans | Consumer | TDR
Troubled Debt Restructuring
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	24,494	24,523
Non-Accruing | Non Covered Loans
Troubled Debt Restructuring
Troubled debt restructurings	272,546	284,558
Non-Accruing | Non Covered Loans | Commercial
Troubled Debt Restructuring
Troubled debt restructurings	120,371	130,921
Non-Accruing | Non Covered Loans | Construction
Troubled Debt Restructuring
Troubled debt restructurings	1,788	1,788
Non-Accruing | Non Covered Loans | Mortgages
Troubled Debt Restructuring
Troubled debt restructurings	134,517	135,758
Non-Accruing | Non Covered Loans | Leasing
Troubled Debt Restructuring
Troubled debt restructurings	313	440
Non-Accruing | Non Covered Loans | Consumer
Troubled Debt Restructuring
Troubled debt restructurings	15,557	15,651
Accruing | Non Covered Loans
Troubled Debt Restructuring
Troubled debt restructurings	1,257,469	1,231,331
Accruing | Non Covered Loans | Commercial
Troubled Debt Restructuring
Troubled debt restructurings	224,648	229,758
Accruing | Non Covered Loans | Construction
Troubled Debt Restructuring
Troubled debt restructurings	0	0
Accruing | Non Covered Loans | Mortgages
Troubled Debt Restructuring
Troubled debt restructurings	939,985	906,712
Accruing | Non Covered Loans | Leasing
Troubled Debt Restructuring
Troubled debt restructurings	705	668
Accruing | Non Covered Loans | Consumer
Troubled Debt Restructuring
Troubled debt restructurings	$ 92,131	$ 94,193