TDRs Differentiated by Loan Type and Accrual Status (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	$ 93,003	$ 67,022
Residential Real Estate
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	44,401	27,130
Class of Financing Receivable
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	93,003	67,022
Class of Financing Receivable | Commercial
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	6,867	4,233
Class of Financing Receivable | Residential Real Estate
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	44,401	27,130
Class of Financing Receivable | Commercial Real Estate
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	37,013	23,540
Class of Financing Receivable | Real Estate Construction
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	4,722	12,119
Loans on non-accrual status | Class of Financing Receivable
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	14,632	6,388
Loans on non-accrual status | Class of Financing Receivable | Commercial
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	2,263
Loans on non-accrual status | Class of Financing Receivable | Residential Real Estate
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	5,625	2,573
Loans on non-accrual status | Class of Financing Receivable | Commercial Real Estate
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	5,149	1,294
Loans on non-accrual status | Class of Financing Receivable | Real Estate Construction
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	1,595	2,521
Accrual Loans | Class of Financing Receivable
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	78,371	60,634
Accrual Loans | Class of Financing Receivable | Commercial
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	4,604	4,233
Accrual Loans | Class of Financing Receivable | Residential Real Estate
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	38,776	24,557
Accrual Loans | Class of Financing Receivable | Commercial Real Estate
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	31,864	22,246
Accrual Loans | Class of Financing Receivable | Real Estate Construction
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings	$ 3,127	$ 9,598