Short-Term Borrowings and Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended			0 Months Ended	9 Months Ended			9 Months Ended					9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011	Apr. 15, 2011 3.875% Convertible Notes	Sep. 30, 2011 3.875% Convertible Notes	Sep. 30, 2012 3.875% Convertible Notes	Dec. 31, 2011 3.875% Convertible Notes	Sep. 30, 2012 Federal Funds Purchased	Sep. 30, 2012 5.70% Senior Notes		Jun. 01, 2012 5.70% Senior Notes	Dec. 31, 2011 5.70% Senior Notes	Sep. 30, 2012 Federal Home Loan Bank Advances	Sep. 30, 2012 Federal Home Loan Bank Advances San Francisco	Sep. 30, 2012 Federal Reserve Bank Advances
Debt Disclosure [Line Items]
Federal Funds Purchased											$ 287,000,000
Interest expense, debt	5,788,000		6,154,000	18,414,000		24,000,000		4,200,000
Weighted average interest rates associated with short-term borrowings	0.17%			0.17%
Senior Notes matured and repaid														141,400,000
Principal value	0	[1]		0	[1]						287,000,000	0				215,000,000
Debt instrument maturity date							Apr. 15, 2011				Oct. 01, 2012	Jun. 01, 2012	[2]			Oct. 01, 2012
Stated interest rate									3.875%	3.875%		5.70%			5.70%
Effective interest rate								5.92%
Market value of collateral pledged																	1,515,246,000	604,537,000
Unused and available funds,FHLB																	1,293,796,000
Unused and available funds																		$ 604,537,000

[1] Represents long-term notes payable related to one of our debt fund investments. The last payment related to the notes was made in April 2012.

[2] 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.