Short-Term Borrowings and Long-Term Debt - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended								12 Months Ended							3 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended
	Nov. 30, 2009	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Special Purpose Trust Entity	Dec. 31, 2010 Special Purpose Trust Entity	Dec. 31, 2009 Special Purpose Trust Entity	Jun. 30, 2011 Interest rate swaps	Sep. 30, 2010 5.375% Senior Notes	Dec. 31, 2011 5.375% Senior Notes	Sep. 30, 2010 3.875% Convertible Notes	Dec. 31, 2011 3.875% Convertible Notes	Dec. 31, 2010 3.875% Convertible Notes	Dec. 31, 2011 3.875% Convertible Notes Hedge and warrant agreement	May 02, 2011 5.70% Senior Notes	Dec. 31, 2011 5.70% Senior Notes		May 15, 2007 5.70% Senior Notes	May 02, 2011 6.05% Subordinated Notes	Dec. 31, 2011 6.05% Subordinated Notes		May 15, 2007 6.05% Subordinated Notes	May 15, 2007 Senior Notes and Subordinated Notes	Dec. 31, 2011 7.0% Junior Subordinated Debentures	Oct. 30, 2003 7.0% Junior Subordinated Debentures	Dec. 31, 2011 Federal Home Loan Bank Advances San Francisco	Dec. 31, 2011 Federal Reserve Bank Advances
Debt Disclosure [Line Items]
Interest expense, debt										$ 30,249,000		$ 28,818,000	$ 27,730,000
Weighted average interest rates associated with short-term borrowings						0.13%						0.13%
Principal value																		350,000,000	350,000,000		250,000,000				141,429,000	[1]	250,000,000		45,964,000	[2]	250,000,000		50,000,000	51,500,000
Discount on issuance of debt																																800,000
Maturity																			Sep. 15, 2020		Apr. 15, 2011				Jun. 01, 2012	[1]			Jun. 01, 2017	[2]			Oct. 15, 2033
Debt instrument, optional maturity date																																		2008-10-30
Aggregate conversion settlement payment																					260,400,000
Payments for settlement of 3.875% Convertible Notes										250,000,000										250,000,000	250,000,000
Debt issuance costs																											2,000,000				2,200,000	4,200,000		2,200,000
Value of common stock shares issued																					10,400,000
Proceeds from issuance of senior notes, net of discount and issuance cost												344,476,000						344,500,000														495,000,000
Number of common stock shares issued	7,965,568																				187,760
Number of shares called																					186,736
Value of stock called																					10,300,000
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																	37,000,000
Net gain from note repurchases and termination of corresponding interest rate swaps										3,123,000	[3]						3,100,000
Price per share of the conversion feature for the hedge and warrant agreement associated with our convertible notes																							$ 64.43
Period of warrants ratable expiration beginning July 15, 2011																							60 days
Convertible notes, effective interest rate																					5.92%	5.70%
Convertible notes, interest expense																					4,200,000	14,100,000
Distributions		7,732,000	7,869,000	9,708,000	13,802,000	14,191,000	10,417,000	9,809,000	9,179,000	39,111,000		43,596,000	49,076,000	3,500,000	3,500,000	3,500,000
Market value of collateral pledged																																			1,500,000,000	100,500,000
Unused and available funds																																				100,500,000
Unused and available funds																																			$ 1,500,000,000

[1] At December 31, 2011 and 2010, included in the carrying value of our 5.70% Senior Notes are $2.6 million and $15.7 million, respectively, related to the fair value of the interest rate swap associated with the notes.

[2] At December 31, 2011 and 2010, included in the carrying value of our 6.05% Subordinated Notes are $8.8 million and $36.3 million, respectively, related to the fair value of the interest rate swap associated with the notes.

[3] Represents gains from the repurchase of $108.6 million of our 5.70% Senior Notes and $204.0 million of our 6.05% Subordinated Notes and the termination of the corresponding portions of interest rate swaps in 2011. For more information, see Note 11-"Short-Term Borrowings and Long-Term Debt."