Long-term Funding (Details) (USD $)	0 Months Ended	3 Months Ended									3 Months Ended
	Sep. 30, 2008	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2008 Subordinated Debt [Member]	Mar. 31, 2012 Senior Notes [Member]	Sep. 30, 2011 Senior Notes [Member]	Mar. 31, 2011 Senior Notes [Member]	Mar. 31, 2012 ASBC Debenture Due 2032 [Member]	Dec. 31, 2011 ASBC Debenture Due 2032 [Member]	Mar. 31, 2012 SFSC Debentures [Member]	Mar. 31, 2012 SFSC Debenture Due 2034 [Member]	Mar. 31, 2012 SFSC Debenture Due 2032 [Member]
Long-term Funding
Federal Home Loan Bank advances		$ 500,409,000	$ 500,476,000
Senior notes ,net		430,000,000	430,000,000
Subordinated debt, net		25,821,000	25,821,000
Junior subordinated debentures, net		211,340,000	211,340,000
Other borrowed funds		9,166,000	9,434,000
Total long-term funding		1,176,736,000	1,177,071,000
Long Term Debt Disclosure [Line Items]
Junior subordinated debentures, net								180,000,000	180,000,000	36,000,000
Carrying value of SFSC subordinated debt				26,000,000		130,000,000	300,000,000			31,000,000
Percentage of interest rate on senior notes					5.125%
Interest Rate of Junior SFSC subordinated debt											90-day LIBOR plus 2.80%	90-day LIBOR plus 3.45%
Interest Rate of Junior SFSC subordinated debt		3.96%									3.35%	3.96%
Long-term Funding (Textuals) [Abstract]
Weighted average interest rate of Long-term advances		1.79%
Fixed coupon interest rate of subordinated debt	9.25%
Junior subordinated debentures issued		$ 180,000,000
Fixed rate of Junior subordinated debt		7.625%