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	Mar. 31, 2014	Dec. 31, 2013
Consumer Heloc [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	$ 251,300	$ 251,102
Consumer Heloc [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	249,156	249,152
Consumer Heloc [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	2,144	1,950
Consumer Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	649,680	620,473
Consumer Auto [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	648,274	618,911
Consumer Auto [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,406	1,562
Consumer - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	96,828	99,683
Consumer - Other [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	95,250	97,877
Consumer - Other [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,578	1,806
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,356,233	1,359,569
Residential [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	1,345,672	1,349,236
Residential [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Finance receivable recorded investment	$ 10,561	$ 10,333