Loans, Leases and Allowance for Credit Losses - Summary of Recorded Investment in Nonaccrual Loans and Loans Past Due 90 Days Still Accruing Interest by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 8,379,319	$ 6,756,249
Past Due/ Delinquent	31,476	54,432
Total Non-accrual	67,659	75,680
Loans past due 90 days or more and still accruing	5,132	1,534
Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	50,893	36,208
Past Due/ Delinquent	16,766	39,472
Total Non-accrual		75,680
Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,731,887	1,555,210
Past Due/ Delinquent	2,730	6,652
Loans past due 90 days or more and still accruing	1,138	887
Commercial real estate [Member] | Owner occupied [Member] | Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	13,630	9,330
Past Due/ Delinquent	0	3,600
Total Non-accrual	13,630	12,930
Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,861,205	1,627,062
Past Due/ Delinquent	14,492	29,388
Loans past due 90 days or more and still accruing	2,171	0
Commercial real estate [Member] | Non-owner occupied [Member] | Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	30,226	17,930
Past Due/ Delinquent	8,601	23,996
Total Non-accrual	38,827	41,926
Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	182,478	186,965
Past Due/ Delinquent	445	0
Loans past due 90 days or more and still accruing	0	0
Commercial real estate [Member] | Multi-family [Member] | Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	0	0
Past Due/ Delinquent	0	0
Total Non-accrual	0	0
Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,325,059	2,232,186
Past Due/ Delinquent	2,570	4,554
Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	204,270	235,618
Past Due/ Delinquent	0	350
Loans past due 90 days or more and still accruing	0	0
Commercial and industrial [Member] | Leases [Member] | Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	373	99
Past Due/ Delinquent	0	350
Total Non-accrual	373	449
Construction and land development [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	392,696	291,883
Past Due/ Delinquent	0	0
Loans past due 90 days or more and still accruing	0	0
Construction and land development [Member] | Construction [Member] | Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	0	0
Past Due/ Delinquent	0	0
Total Non-accrual	0	0
Construction and land development [Member] | Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	358,013	243,741
Past Due/ Delinquent	3,445	1,607
Loans past due 90 days or more and still accruing	805	0
Construction and land development [Member] | Land [Member] | Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,686	3,133
Past Due/ Delinquent	2,640	1,392
Total Non-accrual	5,326	4,525
Residential real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	291,535	339,566
Past Due/ Delinquent	7,337	10,746
Loans past due 90 days or more and still accruing	232	47
Residential real estate [Member] | Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,332	5,067
Past Due/ Delinquent	4,841	7,413
Total Non-accrual	6,173	12,480
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	32,176	44,018
Past Due/ Delinquent	457	1,135
Loans past due 90 days or more and still accruing	83	475
Consumer [Member] | Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	25	27
Past Due/ Delinquent	188	39
Total Non-accrual	$ 213	$ 66