Trust Preferred Securities and Subordinated Debentures (Schedule of Trust Preferred Securities) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Subordinated Borrowing [Line Items]    
Subordinated debentures $ 46,393 $ 46,393
Trust Preferred Securities of the Trusts 45,000 45,000
OKSB Statutory Trust I [Member]    
Subordinated Borrowing [Line Items]    
Subordinated debentures 20,619 20,619
Trust Preferred Securities of the Trusts 20,000 20,000
Rates 3.35% 3.35%
Final Maturity Date Jun. 26, 2033 Jun. 26, 2033
SBI Capital Trust II [Member]    
Subordinated Borrowing [Line Items]    
Subordinated debentures 25,774 25,774
Trust Preferred Securities of the Trusts 25,000 25,000
Rates 3.08% 3.09%
Final Maturity Date Oct. 07, 2033 Oct. 07, 2033
Southwest Capital Trust II [Member]    
Subordinated Borrowing [Line Items]    
Trust Preferred Securities of the Trusts $ 34,500