Derivative Instruments (Details)	6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($) item	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Interest payment period	7 years
Fixed interest rate	6.15%
Rate received by Southwest	3.13%
Pretax loss related to derivative contracts	$ 1,700,000		$ 1,600,000
Gain or loss due to changes in the fair value of the derivative hedging instrument	51,000	$ 42,000
Net cash flows as a result of the interest rate swap agreement	400,000	$ 400,000
Fair Value Net of Cash Collateral	400,000
Interest Rate Swap on Trust Preferred Securities [Member]
Derivative [Line Items]
Interest rate swap agreement Notional amount	$ 25,000,000
Variable interest rate	2.85%
The fair value of cash and securities posted as collateral	$ 2,100,000		2,100,000
Customer Risk Management Swaps [Member]
Derivative [Line Items]
Number of customer interest rate swap agreements | item	3
Interest rate swap agreement Notional amount	$ 33,900,000
Customer Risk Management Swap 1 [Member]
Derivative [Line Items]
Variable interest rate	2.97%
Customer Risk Management Swap 2 [Member]
Derivative [Line Items]
Variable interest rate	2.87%
Customer Risk Management Swap 3 [Member]
Derivative [Line Items]
Variable interest rate	2.30%
Non-Hedge Derivative Asset [Member]
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 33,935,000		34,322,000
Non-hedge derivative asset, fair value	701,000		787,000
Non-Hedge Derivative Liability [Member]
Derivative [Line Items]
Derivative Liability, Notional Amount	33,935,000		34,322,000
Non-hedge derivative liability, fair value	$ 701,000		$ 787,000