Short-Term Borrowings and Long-Term Debt - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended			1 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended			1 Months Ended	6 Months Ended			3 Months Ended
	May 02, 2011	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	May 02, 2011 5.70% Senior Notes	Jun. 30, 2011 5.70% Senior Notes		May 02, 2011 6.05% Subordinated Notes	Jun. 30, 2011 6.05% Subordinated Notes		Jun. 30, 2011 3.875% Convertible Notes	Jun. 30, 2010 3.875% Convertible Notes	Jun. 30, 2011 3.875% Convertible Notes	Jun. 30, 2010 3.875% Convertible Notes	Apr. 15, 2011 3.875% Convertible Notes	Apr. 30, 2008 3.875% Convertible Notes Hedge and warrant agreement	Jun. 30, 2011 3.875% Convertible Notes Hedge and warrant agreement	Jun. 30, 2011 Federal Home Loan Bank Advances San Francisco	Jun. 30, 2011 Federal Reserve Bank Advances	Jun. 30, 2011 Interest rate swaps
Debt Disclosure [Line Items]
Interest expense, debt		$ 7,149,000	$ 5,942,000	$ 17,846,000	$ 11,456,000
Weighted average interest rates associated with short-term borrowings						0.13%
Notes repurchase amount	312,600,000						108,600,000			204,000,000
Gross loss from extinguishment of debt																						(33,900,000)
Gross gain on derivative termination																						36,959,000
Net gain from note repurchases and termination of corresponding interest rate swaps		3,123,000		3,123,000																		3,123,000
Principal value								141,429,000	[1]		45,964,000	[2]					250,000,000
Maturity								Jun. 01, 2012	[1]		Jun. 01, 2017	[2]			Apr. 15, 2011
Aggregate conversion settlement payment															260,400,000
Payments for settlement of 3.875% Convertible Notes				250,000,000											250,000,000
Value of common stock shares issued															10,400,000
Number of common stock shares issued															187,760
Number of shares called															186,736
Value of stock called															10,300,000
Price per share of the conversion feature for the hedge and warrant agreement associated with our convertible notes																		$ 64.43	$ 64.43
Period of warrants ratable expiration																			60 business days beginning on July 15, 2011
Begin date of warrants ratable expiration																			2011-07-15
Convertible notes, effective interest rate													6.84%	5.72%	5.92%	5.75%
Convertible notes, interest expense													700,000	3,500,000	4,200,000	7,100,000
Market value of collateral pledged																				1,600,000,000	96,600,000
Unused and available funds																					96,600,000
Unused and available funds																				$ 1,600,000,000

[1] At June 30, 2011 and December 31, 2010, included in the carrying value of our 5.70% Senior Notes are $6.1 million and $15.7 million, respectively, related to the fair value of the interest rate swap associated with the notes.

[2] At June 30, 2011 and December 31, 2010, included in the carrying value of our 6.05% Subordinated Notes are $7.2 million and $36.3 million, respectively, related to the fair value of the interest rate swap associated with the notes.