Subordinated Debentures (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Subordinated Borrowing [Line Items]
Trust Preferred Securities	$ 45,000,000	$ 79,500,000
Subordinated debentures	46,393,000	81,963,000
Investment in common equity issued by Trusts	1,400,000
OKSB Statutory Trust I [Member]
Subordinated Borrowing [Line Items]
Trust Preferred Securities	20,000,000	20,000,000
Adjustable rate	90-day LIBOR
Adjustable rate, additional percentage	3.10%
Amount of trust common equity sold to Southwest	600,000
Subordinated debentures	20,619,000	20,619,000
Outstanding common securities of the Trust	619
Trust liquidation value per share	$ 1,000
SBI Capital Trust II [Member]
Subordinated Borrowing [Line Items]
Trust Preferred Securities	25,000,000	25,000,000
Adjustable rate	90-day LIBOR
Adjustable rate, additional percentage	2.85%
Amount of trust common equity sold to Southwest	800,000
Subordinated debentures	25,774,000	25,774,000
Outstanding common securities of the Trust	774
Trust liquidation value per share	$ 1,000
Southwest Capital Trust II [Member]
Subordinated Borrowing [Line Items]
Trust Preferred Securities	34,500,000	34,500,000
Adjustable rate, additional percentage	10.50%
Amount of trust common equity sold to Southwest	1,100,000
Subordinated debentures		35,570,000
OKSB Subordinated Debentures [Member]
Subordinated Borrowing [Line Items]
Adjustable rate	90-day LIBOR
Adjustable rate, additional percentage	3.10%
Principal amount of subordinated debentures	20,600,000
SBI II Subordinated Debentures [Member]
Subordinated Borrowing [Line Items]
Adjustable rate, additional percentage	2.85%
Principal amount of subordinated debentures	25,800,000
OKSBP Subordinated Debentures [Member]
Subordinated Borrowing [Line Items]
Adjustable rate, additional percentage	10.50%
Principal amount of subordinated debentures	35,600,000
Trust Preferred Securities [Member]
Subordinated Borrowing [Line Items]
Trust liquidation value per share	$ 25
Tier one capital	$ 45,000,000