Loans and Allowance for Credit Losses - Schedule of Recorded Investment in Residential and Consumer Loans Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Consumer Heloc [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	$ 342,879	$ 251,102
Consumer Heloc [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	340,657	249,152
Consumer Heloc [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	2,222	1,950
Consumer Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	782,341	620,473
Consumer Auto [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	781,151	618,911
Consumer Auto [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,190	1,562
Consumer - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	149,479	99,683
Consumer - Other [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	148,113	97,877
Consumer - Other [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,366	1,806
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,546,939	1,359,569
Residential [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,532,422	1,349,236
Residential [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	$ 14,517	$ 10,333