Loans And Allowance For Loan Losses (Southwest's Loan Classifications) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, Noncovered	$ 1,353,028	$ 1,725,873
Less: Allowance for loan losses	(46,494)	(44,233)
Total loans, net, Noncovered	1,306,534	1,681,640
Loans receivable, Covered	25,707	37,615
Less: Allowance for loan losses, Covered	(224)	(451)
Net covered loans receivable	25,483	37,164
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, Noncovered	240,498	346,266
Loans receivable, Covered	2,037	2,841
Commercial Real Estate [Member] | Real Estate Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, Noncovered	870,975	1,028,561
Loans receivable, Covered	18,298	23,686
Commercial Real Estate [Member] | Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, Noncovered	130,753	227,098
Loans receivable, Covered	382	3,746
One-To-Four Family Residential [Member] | Real Estate Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, Noncovered	70,954	80,375
Loans receivable, Covered	4,881	7,072
One-To-Four Family Residential [Member] | Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, Noncovered	3,656	4,987
Guaranteed Student Loans [Member] | Installment And Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, Noncovered	4,680	5,396
Other [Member] | Installment And Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, Noncovered	31,512	33,190
Loans receivable, Covered	$ 109	$ 270