Derivative Financial Instruments Derivative Financial Instruments (Derivative Asset and Liability Balance Sheet Offsetting) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013
Derivative Assets
Gross Amounts Recognized	$ 37,239		$ 37,956		$ 46,653
Less: Amounts offset in the Statements of Financial Condition	0		0		0
Net amount presented in the Statements of Financial Condition	37,239		37,956		46,653
Offsetting Derivative Positions	(7,359)		(8,826)		(1,523)
Securities Collateral Posted	0	[1]	0	[1]	0	[1]
Cash Collateral Posted	0		0		0
Net Credit Exposure	29,880		29,130		45,130
Derivative Liabilities
Gross Amounts Recognized	34,990		34,807		50,262
Less: Amounts offset in the Statements of Financial Condition	0		0		0
Net amount presented in the Statements of Financial Condition	34,990		34,807		50,262
Offsetting Derivative Positions	(7,359)		(8,826)		(1,523)
Securities Collateral Posted	(27,631)	[1]	(25,981)	[1]	(43,361)	[1]
Cash Collateral Posted	0		0		(2,445)
Net Credit Exposure	$ 0		$ 0		$ 2,933

[1] As of March 31, 2014 and December 31, 2013, the Company posted securities collateral of $37.1 million and $34.6 million, respectively, which resulted in excess collateral with its counterparties. For purposes of this disclosure, the amount of posted collateral is limited to the amount offsetting the derivative liability.