Covered loans past due status (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	$ 2,654,263	$ 2,984,427
Commercial And Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	104,933	102,575
Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	74,468	190,127
Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	846,472	934,373
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	36,672	47,123
Covered Under Loss Sharing Agreements With F D I C [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	77,138	97,691
Financing Receivable Recorded Investment 60 To 89 Days Past Due	44,878	33,806
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	527,632	737,856
Total Past Due	649,648	869,353
Financing Receivable Recorded Investment Current	2,004,615	2,115,074
Covered Loans	2,654,263	2,984,427
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial Real Estate Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	25,957	42,898
Financing Receivable Recorded Investment 60 To 89 Days Past Due	17,189	8,745
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	308,179	374,301
Total Past Due	351,325	425,944
Financing Receivable Recorded Investment Current	1,240,393	1,284,285
Covered Loans	1,591,718	1,710,229
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial And Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	596	1,584
Financing Receivable Recorded Investment 60 To 89 Days Past Due	441	349
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	7,528	16,318
Total Past Due	8,565	18,251
Financing Receivable Recorded Investment Current	96,368	84,324
Covered Loans	104,933	102,575
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	2,461	399
Financing Receivable Recorded Investment 60 To 89 Days Past Due	0	0
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	62,731	178,007
Total Past Due	65,192	178,406
Financing Receivable Recorded Investment Current	9,276	11,721
Covered Loans	74,468	190,127
Covered Under Loss Sharing Agreements With F D I C [Member] | Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	45,980	50,222
Financing Receivable Recorded Investment 60 To 89 Days Past Due	26,465	23,384
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	146,335	165,030
Total Past Due	218,780	238,636
Financing Receivable Recorded Investment Current	627,692	695,737
Covered Loans	846,472	934,373
Covered Under Loss Sharing Agreements With F D I C [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	2,144	2,588
Financing Receivable Recorded Investment 60 To 89 Days Past Due	783	1,328
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	2,859	4,200
Total Past Due	5,786	8,116
Financing Receivable Recorded Investment Current	30,886	39,007
Covered Loans	$ 36,672	$ 47,123