Short-Term Borrowings and Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2011 3.875% Convertible Notes	Jun. 30, 2012 3.875% Convertible Notes	Jun. 30, 2012 5.70% Senior Notes		Jun. 01, 2012 5.70% Senior Notes	Dec. 31, 2011 5.70% Senior Notes	Jun. 30, 2012 Federal Home Loan Bank Advances San Francisco	Jun. 30, 2012 Federal Reserve Bank Advances
Debt Disclosure [Line Items]
Interest expense, debt	$ 6,270,000	$ 7,149,000	$ 12,626,000	$ 17,846,000	$ 700,000	$ 4,200,000
Weighted average interest rates associated with short-term borrowings	0.14%		0.14%
Senior Notes matured and repaid									141,400,000
Principal value						250,000,000
Debt instrument maturity date						Apr. 15, 2011	Jun. 01, 2012	[1]
Stated interest rate						3.875%	5.70%			5.70%
Effective interest rate					6.84%	5.92%
Market value of collateral pledged											1,500,000,000	635,000,000
Unused and available funds,FHLB											1,500,000,000
Unused and available funds												$ 635,000,000

[1] At December 31, 2011, included in the carrying value of our 5.70% Senior Notes was $2.6 million related to the fair value of the interest rate swap associated with the notes.