Covered loans past due status (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	$ 3,199,998	$ 3,755,972
Commercial And Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	114,379	167,236
Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	240,365	361,396
Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	999,578	1,076,730
Consumer Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	59,585	73,199
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	48,488	124,330
Financing Receivable Recorded Investment 60 To 89 Days Past Due	77,486	71,324
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	807,015	1,095,102
Total Past Due	932,989	1,290,756
Financing Receivable Recorded Investment Current	2,267,009	2,465,216
Covered Loans	3,199,998	3,755,972
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	16,036	81,386
Financing Receivable Recorded Investment 60 To 89 Days Past Due	66,737	41,256
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	449,458	545,241
Total Past Due	532,231	667,883
Financing Receivable Recorded Investment Current	1,253,860	1,409,528
Covered Loans	1,786,091	2,077,411
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	1,615	3,242
Financing Receivable Recorded Investment 60 To 89 Days Past Due	227	551
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	18,184	59,554
Total Past Due	20,026	63,347
Financing Receivable Recorded Investment Current	94,353	103,889
Covered Loans	114,379	167,236
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	881	13
Financing Receivable Recorded Investment 60 To 89 Days Past Due	0	0
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	228,754	296,837
Total Past Due	229,635	296,850
Financing Receivable Recorded Investment Current	10,730	64,546
Covered Loans	240,365	361,396
Covered Under Loss Sharing Agreements With F D I C [Member] | Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	28,949	38,307
Financing Receivable Recorded Investment 60 To 89 Days Past Due	10,136	28,206
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	107,274	182,376
Total Past Due	146,359	248,889
Financing Receivable Recorded Investment Current	853,219	827,841
Covered Loans	999,578	1,076,730
Covered Under Loss Sharing Agreements With F D I C [Member] | Consumer Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	1,007	1,382
Financing Receivable Recorded Investment 60 To 89 Days Past Due	386	1,311
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	3,345	11,094
Total Past Due	4,738	13,787
Financing Receivable Recorded Investment Current	54,847	59,412
Covered Loans	$ 59,585	$ 73,199