Loans - Past Due, Non-Accrual and Current Non-Covered Loans by Loan Portfolio Class (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	$ 62,100	$ 55,757
Total Past Due Loans	88,240	86,987
Current Non-PCI Loans	13,714,396	11,665,125
Total Non-PCI Loans	13,802,636	11,752,112
30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	18,509	20,198
60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	5,575	5,554
Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,056	5,478
Commercial and industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	10,913	8,467
Total Past Due Loans	15,570	11,425
Current Non-PCI Loans	2,140,979	1,948,502
Total Non-PCI Loans	2,156,549	1,959,927
Commercial and industrial [Member] | 30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,920	1,630
Commercial and industrial [Member] | 60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	524	1,102
Commercial and industrial [Member] | Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	213	226
Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	31,051	27,321
Total Past Due Loans	38,541	40,857
Current Non-PCI Loans	6,638,685	5,488,979
Total Non-PCI Loans	6,677,226	5,529,836
Commercial real estate [Member] | 30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4,560	9,386
Commercial real estate [Member] | 60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,799	113
Commercial real estate [Member] | Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	131	4,037
Commercial real estate [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	24,888	22,098
Total Past Due Loans	27,703	31,198
Current Non-PCI Loans	6,041,829	5,022,544
Total Non-PCI Loans	6,069,532	5,053,742
Commercial real estate [Member] | Commercial real estate [Member] | 30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,684	8,938
Commercial real estate [Member] | Commercial real estate [Member] | 60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	113
Commercial real estate [Member] | Commercial real estate [Member] | Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	131	49
Commercial real estate [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	6,163	5,223
Total Past Due Loans	10,838	9,659
Current Non-PCI Loans	596,856	466,435
Total Non-PCI Loans	607,694	476,094
Commercial real estate [Member] | Construction [Member] | 30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,876	448
Commercial real estate [Member] | Construction [Member] | 60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,799	0
Commercial real estate [Member] | Construction [Member] | Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	3,988
Residential mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	17,930	17,760
Total Past Due Loans	27,741	28,598
Current Non-PCI Loans	2,884,338	2,390,446
Total Non-PCI Loans	2,912,079	2,419,044
Residential mortgage [Member] | 30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	6,681	6,200
Residential mortgage [Member] | 60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,626	3,575
Residential mortgage [Member] | Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,504	1,063
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	2,206	2,209
Total Past Due Loans	6,388	6,107
Current Non-PCI Loans	2,050,394	1,837,198
Total Non-PCI Loans	2,056,782	1,843,305
Consumer [Member] | 30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,348	2,982
Consumer [Member] | 60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	626	764
Consumer [Member] | Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	208	152
Consumer [Member] | Home equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	2,088	2,022
Total Past Due Loans	3,507	3,065
Current Non-PCI Loans	388,302	397,071
Total Non-PCI Loans	391,809	400,136
Consumer [Member] | Home equity [Member] | 30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,308	761
Consumer [Member] | Home equity [Member] | 60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	111	282
Consumer [Member] | Home equity [Member] | Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	0
Consumer [Member] | Automobile [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	118	90
Total Past Due Loans	2,742	2,509
Current Non-PCI Loans	1,236,084	1,142,271
Total Non-PCI Loans	1,238,826	1,144,780
Consumer [Member] | Automobile [Member] | 30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,969	1,902
Consumer [Member] | Automobile [Member] | 60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	491	391
Consumer [Member] | Automobile [Member] | Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	164	126
Consumer [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	0	97
Total Past Due Loans	139	533
Current Non-PCI Loans	426,008	297,856
Total Non-PCI Loans	426,147	298,389
Consumer [Member] | Other consumer [Member] | 30 to 59 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	71	319
Consumer [Member] | Other consumer [Member] | 60 to 89 Days Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	24	91
Consumer [Member] | Other consumer [Member] | Accruing Loans 90 Days Or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	$ 44	$ 26