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	Jun. 30, 2014	Dec. 31, 2013
Consumer Heloc [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	$ 281,823	$ 251,102
Consumer Heloc [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	279,809	249,152
Consumer Heloc [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	2,014	1,950
Consumer Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	696,009	620,473
Consumer Auto [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	694,924	618,911
Consumer Auto [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,085	1,562
Consumer - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	111,176	99,683
Consumer - Other [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	109,917	97,877
Consumer - Other [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,259	1,806
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,425,179	1,359,569
Residential [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,413,778	1,349,236
Residential [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	$ 11,401	$ 10,333