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	Sep. 30, 2014	Dec. 31, 2013
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	$ 94,254	$ 56,311
Securities Purchased Under Agreements to Resell	5,115	19,134
Securities Sold Under Agreements to Repurchase	(99,484)	(75,563)
Asset (Liability) Balance [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	94,254	56,311
Securities Purchased Under Agreements to Resell	5,115	19,134
Total Assets	99,369	75,445
Securities Sold Under Agreements to Repurchase	(99,484)	(75,563)
Market Value of Collateral Received or (Pledged) [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Purchased Under Agreements to Resell	5,137	19,112
Securities Sold Under Agreements to Repurchase	$ (99,573)	$ (75,708)