Financial Instruments Owned and Pledged as Collateral at Fair Value, Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase Summary of Assets, Liabilities and Collateral Received or Pledged (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	$ 56,311	$ 120,594
Securities Purchased Under Agreements to Resell	19,134	0
Securities Sold Under Agreements to Repurchase	(75,563)	(120,787)
Asset (Liability) Balance [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	56,311	120,594
Securities Purchased Under Agreements to Resell	19,134	0
Total Assets	75,445	120,594
Securities Sold Under Agreements to Repurchase	(75,563)	(120,787)
Market Value of Collateral Received or (Pledged) [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Purchased Under Agreements to Resell	19,112	0
Securities Sold Under Agreements to Repurchase	$ (75,708)	$ (121,029)