Short-Term Borrowings and Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended							1 Months Ended	12 Months Ended		0 Months Ended		0 Months Ended		12 Months Ended		1 Months Ended							12 Months Ended			12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2013 Special Purpose Trust Entity	Dec. 31, 2012 Special Purpose Trust Entity	Dec. 31, 2011 Special Purpose Trust Entity	Sep. 30, 2010 5.375% Senior Notes	Dec. 31, 2013 5.375% Senior Notes	Dec. 31, 2012 5.375% Senior Notes	Apr. 15, 2011 3.875% Convertible Notes	Dec. 31, 2011 3.875% Convertible Notes	Jul. 15, 2011 3.875% Convertible Notes Hedge and warrant agreement	Apr. 15, 2011 3.875% Convertible Notes Hedge and warrant agreement	Dec. 31, 2012 3.875% Convertible Notes Hedge and warrant agreement	Dec. 31, 2011 5.70% Senior Notes	May 02, 2011 6.05% Subordinated Notes	May 15, 2007 6.05% Subordinated Notes	Dec. 31, 2013 7.0% Junior Subordinated Debentures	Oct. 30, 2003 7.0% Junior Subordinated Debentures	Dec. 31, 2013 Federal Funds Purchased	Dec. 31, 2013 Federal Home Loan Bank Advances San Francisco	Dec. 31, 2013 Federal Reserve Bank Advances	Dec. 31, 2013 6.05% Subordinated Notes		Dec. 31, 2012 6.05% Subordinated Notes	Dec. 31, 2013 7.0% Junior Subordinated Debentures	Dec. 31, 2012 7.0% Junior Subordinated Debentures
Debt Disclosure [Line Items]
Stated interest rate																	5.375%	5.375%		3.875%				5.70%								6.05%		6.05%	7.00%	7.00%
Interest expense, debt									$ 23,149,000	$ 24,194,000	$ 30,249,000
Weighted average interest rates associated with short-term borrowings	0.08%								0.08%
Principal value																350,000,000	350,000,000		250,000,000								50,000,000		0			45,964,000	[1]		50,000,000
Discount on issuance of debt																										250,000,000
Maturity																	Sep. 15, 2020	Sep. 15, 2020	Apr. 15, 2011													Jun. 01, 2017			Oct. 15, 2033	Oct. 15, 2033
Aggregate conversion settlement payment																			260,000,000
Payments for settlement of 3.875% Convertible Notes									0	0	250,000,000							250,000,000	250,000,000
Debt issuance costs																												2,200,000
Value of common stock shares issued																			10,000,000
Proceeds from issuance of senior notes, net of discount and issuance cost																345,000,000
Number of common stock shares issued																			187,760
Number of shares called																			186,736
Value of stock called																						10,000,000
Notes repurchase amount																									204,000,000
Net gain from note repurchases and termination of corresponding interest rate swaps									0	0	3,123,000	[2]
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
Distributions	8,386,000	8,144,000	7,902,000	7,845,000	7,605,000	7,528,000	7,884,000	7,837,000	32,277,000	30,854,000	39,111,000		3,500,000	3,500,000	3,500,000
Market value of collateral pledged																														1,400,000,000	578,000,000
Unused and available funds
Unused and available funds

[1] At December 31, 2013 and 2012, included in the carrying value of our 6.05% Subordinated Notes were $6 million and $9 million, respectively, related to hedge accounting associated with the notes.

[2] Represents gains from the repurchase of $109 million of our 5.70% Senior Notes and $204 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."