Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Narrative) (Detail) (USD $)	3 Months Ended				9 Months Ended				12 Months Ended				3 Months Ended		9 Months Ended			3 Months Ended				9 Months Ended
	Sep. 30, 2013 Loan		Sep. 30, 2012 Loan		Sep. 30, 2013 Loan		Sep. 30, 2012 Loan		Sep. 30, 2013 Loan		Sep. 30, 2012 Loan		Sep. 30, 2013 Financing Receivable [Member]	Sep. 30, 2012 Financing Receivable [Member]	Sep. 30, 2013 Financing Receivable [Member] credits	Sep. 30, 2012 Financing Receivable [Member]	Dec. 31, 2012 Financing Receivable [Member]	Sep. 30, 2013 Modification to Interest Only Payments [Member] Loan		Sep. 30, 2012 Modification to Interest Only Payments [Member] Loan		Sep. 30, 2013 Modification to Interest Only Payments [Member] Loan		Sep. 30, 2012 Modification to Interest Only Payments [Member] Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Restructured loans													$ 115,003,000	$ 147,196,000	$ 115,003,000	$ 147,196,000	$ 126,473,000
Troubled debt restructuring modifications, number of count	4	[1],[2]	18	[1],[2]	30	[1],[2]	68	[1],[2]	37	[1],[3]	121	[1],[3]			161			0	[1]	11	[1]	7	[1]	41	[1]
Allowance for loan losses related to impaired loans	14,329,000				14,329,000				14,329,000				4,400,000	19,818,000	4,400,000	19,818,000	13,575,000
Interest income													205,000	534,000	727,000	1,000,000
Restructured loans	4,003,000	[1],[2]	9,516,000	[1],[2]	20,748,000	[1],[2]	69,853,000	[1],[2]	23,407,000	[1],[3]	114,404,000	[1],[3]						0	[1]	8,475,000	[1]	6,539,000	[1]	56,383,000	[1]
Weighted average extension term	26 months		8 months		19 months		8 months
Weighted average interest only term			9 months		11 months		5 months
Loan forgiveness	$ 1,000,000		$ 0		$ 1,000,000		$ 420,000
Weighted average stated interest rate, basis points	1.50%		2.93%		1.99%		1.51%

[1] Balances represent the recorded investment in the loan at the time of the restructuring.

[2] TDRs may have more than one modification representing a concession. As such, TDRs during the period may be represented in more than one of the categories noted above.

[3] Total TDRs represent all loans restructured in TDRs during the previous twelve months from the date indicated.