Covered loans past due status (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	$ 3,076,009	$ 3,755,972
Commercial And Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	128,698	167,236
Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	201,437	361,396
Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	965,779	1,076,730
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	54,942	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	53,558	124,330
Financing Receivable Recorded Investment 60 To 89 Days Past Due	32,793	71,324
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	787,509	1,095,102
Total Past Due	873,860	1,290,756
Financing Receivable Recorded Investment Current	2,202,149	2,465,216
Covered Loans	3,076,009	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	18,765	81,386
Financing Receivable Recorded Investment 60 To 89 Days Past Due	11,876	41,256
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	469,107	545,241
Total Past Due	499,748	667,883
Financing Receivable Recorded Investment Current	1,225,405	1,409,528
Covered Loans	1,725,153	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	1,516	3,242
Financing Receivable Recorded Investment 60 To 89 Days Past Due	800	551
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	16,718	59,554
Total Past Due	19,034	63,347
Financing Receivable Recorded Investment Current	109,664	103,889
Covered Loans	128,698	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	0	13
Financing Receivable Recorded Investment 60 To 89 Days Past Due	160	0
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	189,612	296,837
Total Past Due	189,772	296,850
Financing Receivable Recorded Investment Current	11,665	64,546
Covered Loans	201,437	361,396
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	32,205	38,307
Financing Receivable Recorded Investment 60 To 89 Days Past Due	19,268	28,206
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	109,373	182,376
Total Past Due	160,846	248,889
Financing Receivable Recorded Investment Current	804,933	827,841
Covered Loans	965,779	1,076,730
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	1,072	1,382
Financing Receivable Recorded Investment 60 To 89 Days Past Due	689	1,311
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	2,699	11,094
Total Past Due	4,460	13,787
Financing Receivable Recorded Investment Current	50,482	59,412
Covered Loans	$ 54,942	$ 73,199