Long-term Funding (Details) (USD $)	1 Months Ended		3 Months Ended		6 Months Ended
	Sep. 30, 2008	Aug. 31, 2001	Mar. 31, 2011	Sep. 30, 2010	Jun. 30, 2011	Aug. 15, 2011	Dec. 31, 2010
Long-term Funding
Federal Home Loan Bank advances					$ 800,502,000		$ 1,000,528,000
Senior notes ,net					298,663,000		0
Subordinated debt, net					167,531,000		195,436,000
Junior subordinated debentures, net					215,738,000		215,848,000
Other borrowed funds					1,740,000		1,793,000
Total long-term funding					1,484,174,000		1,413,605,000
Long-term Funding (Textuals) [Abstract]
Debentures redeemed during period value					0
Weighted average interest rate of Long-term advances					1.58%		1.66%
Maturity period of Subordinated debt	10 years	10 years
Period of no-call provision of Subordinated debt	5 years
Fixed coupon interest rate of subordinated debt	9.25%	6.75%
Penalty paid on early extinguishment of Subordinated debt			600,000	700,000
Outstanding balance of matured subordinated debt						142,000,000
Junior subordinated debentures issued					180,400,000
Fixed rate of Junior subordinated debt					7.625%
Subordinated Debt [Member]
Long Term Debt Disclosure [Line Items]
Discounting period of debt					5 year or less
Retirement of Subordinated debt			28,000,000	30,000,000
Carrying value of SFSC subordinated debt	26,000,000	200,000,000
Senior Notes [Member]
Long Term Debt Disclosure [Line Items]
Carrying value of SFSC subordinated debt			300,000,000
Percentage of interest rate on senior notes					5.125%
ASBC Debenture Due 2032 [Member]
Long Term Debt Disclosure [Line Items]
Junior subordinated debentures, net					179,700,000		179,700,000
SFSC Debentures [Member]
Long Term Debt Disclosure [Line Items]
Junior subordinated debentures, net					36,100,000		36,200,000
Carrying value of SFSC subordinated debt					$ 30,900,000
SFSC Debenture Due 2034 [Member]
Long Term Debt Disclosure [Line Items]
Interest Rate of Junior SFSC subordinated debt					90 Day LIBOR Plus 2.80%
Interest Rate of Junior SFSC subordinated debt					3.07%
SFSC Debenture Due 2032 [Member]
Long Term Debt Disclosure [Line Items]
Interest Rate of Junior SFSC subordinated debt					90 Day LIBOR Plus 3.45%
Interest Rate of Junior SFSC subordinated debt					3.71%