Premises and equipment - Summary of Premises and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Land	$ 84,545	$ 86,120
Leasehold improvements	198,498	198,379
Premises and equipment, Gross	1,160,729	1,096,327
Less: accumulated depreciation and amortization	566,077	514,892
Premises and equipment, net	594,652	581,435
Owned assets [Member]
Property, Plant and Equipment [Line Items]
Buildings	393,527	365,087
Furniture and equipment	465,113	436,203
Less: accumulated depreciation and amortization	559,948	512,399
Capital leases [Member]
Property, Plant and Equipment [Line Items]
Buildings	1,131	1,131
Furniture and equipment	17,915	9,407
Less: accumulated depreciation and amortization	$ 6,129	$ 2,493