Loans and Allowance for Credit Losses - Schedule of Past Due Financing Receivables (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded Investment > 90 Days and Accruing	$ 670	$ 916
Nonaccrual	160,340	132,373
Financing Receivables, Past Due	194,981	153,645
Current	8,635,177	6,794,760
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	27,995	16,266
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	5,976	4,090
Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded Investment > 90 Days and Accruing	175	565
Nonaccrual	54,554	57,536
Financing Receivables, Past Due	55,452	59,003
Current	1,838,248	1,745,612
Commercial Loan [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	496	802
Commercial Loan [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	227	100
Construction [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	1,483	749
Financing Receivables, Past Due	1,483	749
Current	262,013	184,700
Other [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	74,247	46,601
Financing Receivables, Past Due	76,026	47,174
Current	2,604,003	1,615,198
Other [Member] | Commercial Real Estate [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	1,779	438
Other [Member] | Commercial Real Estate [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due		135
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded Investment > 90 Days and Accruing	101	114
Nonaccrual	17,185	14,953
Financing Receivables, Past Due	33,233	26,613
Current	2,066,537	1,618,001
Residential [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	14,221	9,300
Residential [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	1,726	2,246
Consumer Heloc [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded Investment > 90 Days and Accruing	240
Nonaccrual	3,839	2,369
Financing Receivables, Past Due	5,585	3,054
Current	467,965	356,900
Consumer Heloc [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	1,286	283
Consumer Heloc [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	220	402
Consumer Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded Investment > 90 Days and Accruing	104	202
Nonaccrual	1,266	1,573
Financing Receivables, Past Due	5,016	6,309
Current	1,140,182	1,044,027
Consumer Auto [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	2,962	3,804
Consumer Auto [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	684	730
Consumer - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded Investment > 90 Days and Accruing	50	25
Nonaccrual	7,766	1,256
Financing Receivables, Past Due	18,186	2,276
Current	256,229	131,202
Consumer - Other [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	7,251	830
Consumer - Other [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	$ 3,119	165
Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded Investment > 90 Days and Accruing		10
Nonaccrual		7,336
Financing Receivables, Past Due		8,467
Current		99,120
Covered Loans [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due		809
Covered Loans [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due		$ 312