Loans - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Period within which commitments are to be disbursed			60 days
Allowance for loan losses charge offs		$ 38,200,000
Amounts charged off	1,104,000	3,882,000	7,854,000	22,946,000	0
Maximum period after which troubled debt restructuring is considered to be in payment by default			30 days
Effect of troubled debt restructurings on provision for loan losses			0
Total Recorded Investment	46,327,000	59,244,000	46,327,000	59,244,000	61,017,000
Period of cumulative homogeneous loans past due included in company analysis			90 days
Maximum duration under which loans may be housed under Special Mention category			No Longer Than 12 Months
Troubled Debt Restructurings [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Increment in allowance for loan losses	206,000	367,000	778,000	367,000
Amounts charged off	0	0	1,800,000	0
Total Recorded Investment	$ 15,900,000		$ 15,900,000