Fair Value (Details) (USD $)	3 Months Ended									3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended																																																													3 Months Ended				3 Months Ended			3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Change During Period, Fair Value Disclosure [Member]	Mar. 31, 2012 Change During Period, Fair Value Disclosure [Member]	Mar. 31, 2013 MBS	Dec. 31, 2012 MBS	Mar. 31, 2013 Municipal Bonds	Dec. 31, 2012 Municipal Bonds	Mar. 31, 2013 Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Mar. 31, 2013 Fair Value, Measurements, Nonrecurring [Member] Loans [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Loans [Member] Carrying Amount [Member]	Mar. 31, 2013 Fair Value, Measurements, Nonrecurring [Member] OREO [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] OREO [Member]	Mar. 31, 2013 Fair Value, Measurements, Nonrecurring [Member] OREO [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] OREO [Member] Carrying Amount [Member]	Mar. 31, 2013 Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Mar. 31, 2013 Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member] Carrying Amount [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] MBS	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] MBS	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Carrying Amount [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] MBS	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] MBS	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] OREO [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] OREO [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Carrying Amount [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] MBS	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] MBS	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] OREO [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] OREO [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Carrying Amount [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] MBS	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] MBS	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member] Minimum [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member] Maximum [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] OREO [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] OREO [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] OREO [Member] Minimum [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] OREO [Member] Maximum [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member] Minimum [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member] Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Inputs, Selling Costs, Percent																																																																																4.50%	9.00%			4.50%	9.00%
Cash and cash equivalents																														$ 297,210,000	$ 331,550,000	$ 297,210,000	$ 331,550,000
Available for sale	1,471,563,000		1,513,157,000			1,268,330,000	1,308,838,000	203,063,000	204,306,000													1,471,563,000	1,513,157,000	1,268,330,000	1,308,838,000	203,063,000	204,306,000	170,000	13,000					0	0	0	0	0	0	0	0							1,471,563,000	1,513,157,000	1,471,563,000	1,513,157,000	1,471,563,000	1,513,157,000	1,268,330,000	1,308,838,000	203,063,000	204,306,000	170,000	13,000											0	0	0	0	0	0	0	0
Held to maturity																																																195,000	206,000	195,000	206,000
Loans held for sale				(10,189,000)	(1,589,000)																	295,505,000	465,983,000											0	0													295,505,000	465,983,000	295,505,000	465,983,000																			0	0
Loans Receivable Held-for-sale, Net	295,505,000		465,983,000																																																	295,505,000	465,983,000
Loans receivable, net												56,794,000	172,172,000																													0	0																	0	0					6,334,560,000	6,101,749,000	6,383,034,000	6,154,296,000									56,794,000	172,172,000
Gain (Loss) on Mortgage Servicing Rights	2,834,000	2,216,000																2,834,000	(230,000)
Gain (Loss) on Sales of Loans, Net										(3,813,000)	(27,649,000)
Other Real Estate Fair Value Disclosure																13,772,000	18,074,000																											0	0																	0	0																			13,772,000	18,074,000
Gains (Losses) on Sales of Other Real Estate	(214,000)	752,000												(1,630,000)	(1,296,000)
Servicing Asset at Fair Value, Amount																				45,061,000	32,420,000																									0	0																	0	0			46,009,000	32,420,000
Mortgage servicing rights, net	45,061,000		32,420,000																																																															45,061,000	32,420,000																			45,061,000
Other assets																						9,307,000	11,183,000											0	0													106,335,000	108,642,000	106,335,000	108,642,000	9,307,000	11,183,000																	0	0
Assets, Fair Value Disclosure, Recurring																						1,776,375,000	1,990,323,000											0	0																	1,776,375,000	1,990,323,000																	0	0
Other liabilities - derivatives																						4,349,000	4,025,000											0	0																	4,349,000	4,025,000																	0	0
Total liabilities																						13,539,000	19,467,000											0	0																	4,349,000	4,025,000																	9,190,000	15,442,000
Non-maturity deposits																																																4,857,423,000	4,697,147,000	4,857,423,000	4,697,147,000
Deposits with stated maturities																																																1,740,415,000	1,738,970,000	1,765,301,000	1,768,818,000
Borrowings																																																1,317,620,000	1,437,491,000	1,335,093,000	1,457,911,000
Other liabilities																																																4,349,000	4,025,000	4,349,000	4,025,000
FHLB stock	97,000,000		97,500,000
Charge-offs for properties held	2,600,000	3,900,000
Weighted average prepayment speed																																																																																							5.00%	19.40%
Contingent Consideration Liability [Roll Forward]
Beginning Balance	15,442,000	0																				9,190,000	15,442,000											0	0																	0	0																	9,190,000	15,442,000
Additions	0	11,779,000
Valuation adjustments	586,000	0
stsa_CashPaidContingentConsideration	(6,838,000)	0
Ending Balance		$ 11,779,000																				$ 9,190,000	$ 15,442,000											$ 0	$ 0																	$ 0	$ 0																	$ 9,190,000	$ 15,442,000
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Discount Rate																																																																																							10.20%	20.00%