Loans - Past Due, Non-Accrual and Current Non-Covered Loans by Loan Portfolio Class (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	$ 14,282	$ 27,113
60-89 Days Past Due Loans	4,788	10,313
Accruing Loans 90 Days Or More Past Due	12,476	9,491
Non-Accrual Loans	59,893	95,063
Total Past Due Loans	91,439	141,980
Current Non-PCI Loans	11,444,250	10,619,364
Total Non-PCI Loans	11,535,689	10,761,344
Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	1,194	10,328
60-89 Days Past Due Loans	942	7,019
Accruing Loans 90 Days Or More Past Due	9,885	7,591
Non-Accrual Loans	32,957	52,050
Total Past Due Loans	44,978	76,988
Current Non-PCI Loans	5,358,153	4,851,809
Total Non-PCI Loans	5,403,131	4,928,797
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	3,741	3,792
60-89 Days Past Due Loans	913	784
Accruing Loans 90 Days Or More Past Due	278	118
Non-Accrual Loans	2,380	2,035
Total Past Due Loans	7,312	6,729
Current Non-PCI Loans	1,760,732	1,520,443
Total Non-PCI Loans	1,768,044	1,527,172
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	476	6,398
60-89 Days Past Due Loans	629	571
Accruing Loans 90 Days Or More Past Due	256	233
Non-Accrual Loans	7,251	21,029
Total Past Due Loans	8,612	28,231
Current Non-PCI Loans	1,932,858	1,791,905
Total Non-PCI Loans	1,941,470	1,820,136
Commercial Real Estate [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	1,194	9,142
60-89 Days Past Due Loans	788	2,442
Accruing Loans 90 Days Or More Past Due	52	7,591
Non-Accrual Loans	26,379	43,934
Total Past Due Loans	28,413	63,109
Current Non-PCI Loans	4,933,577	4,458,811
Total Non-PCI Loans	4,961,990	4,521,920
Construction [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	0	1,186
60-89 Days Past Due Loans	154	4,577
Accruing Loans 90 Days Or More Past Due	9,833	0
Non-Accrual Loans	6,578	8,116
Total Past Due Loans	16,565	13,879
Current Non-PCI Loans	424,576	392,998
Total Non-PCI Loans	441,141	406,877
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	8,871	6,595
60-89 Days Past Due Loans	2,304	1,939
Accruing Loans 90 Days Or More Past Due	2,057	1,549
Non-Accrual Loans	17,305	19,949
Total Past Due Loans	30,537	30,032
Current Non-PCI Loans	2,392,507	2,455,207
Total Non-PCI Loans	2,423,044	2,485,239
Home Equity [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	1,817	495
60-89 Days Past Due Loans	198	241
Accruing Loans 90 Days Or More Past Due	0	0
Non-Accrual Loans	2,285	1,866
Total Past Due Loans	4,300	2,602
Current Non-PCI Loans	396,772	408,273
Total Non-PCI Loans	401,072	410,875
Automobile [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	1,800	2,957
60-89 Days Past Due Loans	524	489
Accruing Loans 90 Days Or More Past Due	246	85
Non-Accrual Loans	95	169
Total Past Due Loans	2,665	3,700
Current Non-PCI Loans	1,088,622	897,699
Total Non-PCI Loans	1,091,287	901,399
Other Consumer [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due Loans	124	340
60-89 Days Past Due Loans	191	54
Accruing Loans 90 Days Or More Past Due	32	33
Non-Accrual Loans	0	0
Total Past Due Loans	347	427
Current Non-PCI Loans	275,338	214,471
Total Non-PCI Loans	$ 275,685	$ 214,898