Fair Value Measurements (Narrative) (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]    
Private equity investment Southwest's proportionate share of the net asset value $ 0 $ 2,400,000
Impairment charges 0 0
Noncovered [Member]    
Finite-Lived Intangible Assets [Line Items]    
Noncovered impaired loans carrying amount 21,900,000 47,000,000
Noncovered impaired loans measured at fair value 17,500,000 33,700,000
Noncovered impaired loans life to date impairment 4,400,000 13,300,000
Impairment charge of other real estate assets $ 600,000 $ 2,200,000