Subordinated Debentures (Schedule of Trust Preferred Securities) (Details) (USD $) In Thousands, unless otherwise specified			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 OKSB Statutory Trust I [Member]	Dec. 31, 2012 SBI Capital Trust II [Member]	Dec. 31, 2012 Southwest Capital Trust II [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures	$ 81,963	$ 81,963	$ 20,619	$ 25,774	$ 35,570
Trust Preferred Securities of the Trusts	$ 79,500		$ 20,000	$ 25,000	$ 34,500
Rates			3.41%	3.19%	10.50%
Final Maturity Date			Jun. 26, 2033	Oct. 07, 2033	Sep. 15, 2038