Covered loans past due status (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	$ 2,870,054	$ 2,984,427
Commercial And Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	107,551	102,575
Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	127,444	190,127
Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	907,069	934,373
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	43,856	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	96,417	97,691
Financing Receivable Recorded Investment 60 To 89 Days Past Due	21,685	33,806
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	653,487	737,856
Total Past Due	771,589	869,353
Financing Receivable Recorded Investment Current	2,098,465	2,115,074
Covered Loans	2,870,054	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	32,837	42,898
Financing Receivable Recorded Investment 60 To 89 Days Past Due	4,819	8,745
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	368,923	374,301
Total Past Due	406,579	425,944
Financing Receivable Recorded Investment Current	1,277,555	1,284,285
Covered Loans	1,684,134	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	1,160	1,584
Financing Receivable Recorded Investment 60 To 89 Days Past Due	862	349
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	8,378	16,318
Total Past Due	10,400	18,251
Financing Receivable Recorded Investment Current	97,151	84,324
Covered Loans	107,551	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	0	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	115,978	178,007
Total Past Due	115,978	178,406
Financing Receivable Recorded Investment Current	11,466	11,721
Covered Loans	127,444	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	60,074	50,222
Financing Receivable Recorded Investment 60 To 89 Days Past Due	14,979	23,384
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	156,194	165,030
Total Past Due	231,247	238,636
Financing Receivable Recorded Investment Current	675,822	695,737
Covered Loans	907,069	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	2,346	2,588
Financing Receivable Recorded Investment 60 To 89 Days Past Due	1,025	1,328
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	4,014	4,200
Total Past Due	7,385	8,116
Financing Receivable Recorded Investment Current	36,471	39,007
Covered Loans	$ 43,856	$ 47,123