Covered loans past due status (Detail) - Entity [Domain] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	$ 689,650	$ 2,542,662
Commercial And Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	0	103,309
Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	0	70,336
Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	671,074	822,986
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Covered Loans	18,573	34,559
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	6,233	146,719
Financing Receivable Recorded Investment 60 To 89 Days Past Due	17,253	37,266
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	97,331	503,103
Total Past Due	120,817	687,088
Financing Receivable Recorded Investment Current	568,833	1,855,574
Covered Loans	689,650	2,542,662
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	0	98,559
Financing Receivable Recorded Investment 60 To 89 Days Past Due	0	12,597
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	3	291,010
Total Past Due	3	402,166
Financing Receivable Recorded Investment Current	0	1,109,306
Covered Loans	3	1,511,472
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	0	512
Financing Receivable Recorded Investment 60 To 89 Days Past Due	0	7
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	0	7,756
Total Past Due	0	8,275
Financing Receivable Recorded Investment Current	0	95,034
Covered Loans	0	103,309
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	0
Financing Receivable Recorded Investment 60 To 89 Days Past Due	0	384
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	0	58,665
Total Past Due	0	59,049
Financing Receivable Recorded Investment Current	0	11,287
Covered Loans	0	70,336
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	6,223	45,764
Financing Receivable Recorded Investment 60 To 89 Days Past Due	16,771	23,531
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	96,097	143,140
Total Past Due	119,091	212,435
Financing Receivable Recorded Investment Current	551,983	610,551
Covered Loans	671,074	822,986
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	10	1,884
Financing Receivable Recorded Investment 60 To 89 Days Past Due	482	747
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	1,231	2,532
Total Past Due	1,723	5,163
Financing Receivable Recorded Investment Current	16,850	29,396
Covered Loans	$ 18,573	$ 34,559