Subordinated Debentures (Narrative) (Details) (USD $)			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]	Dec. 31, 2012 OKSB Subordinated Debentures [Member]	Dec. 31, 2012 SBI II Subordinated Debentures [Member]	Dec. 31, 2012 OKSBP Subordinated Debentures [Member]	Dec. 31, 2012 Trust Preferred Securities [Member]
Subordinated Borrowing [Line Items]
Trust Preferred Securities	$ 79,500,000		$ 20,000,000	$ 25,000,000	$ 34,500,000
Adjustable rate			90-day LIBOR	90-day LIBOR		90-day LIBOR
Adjustable rate, additional percentage			3.10%	2.85%	10.50%	3.10%	2.85%	10.50%
Amount of trust common equity sold to Southwest			600,000	800,000	1,100,000
Principal amount of subordinated debentures						20,600,000	25,800,000	35,600,000
Subordinated debentures	81,963,000	81,963,000	20,619,000	25,774,000	35,570,000
Investment in common equity issued by Trusts	2,500,000
Outstanding common securities of the Trust			619	774	42,800
Trust liquidation value per share			$ 1,000	$ 1,000	$ 25
Tier one capital									$ 79,500,000