Investment Securities, Amortized Cost, Maturities and Approximate Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Amortized Cost [Abstract]
Due in one year or less	$ 28,985
Due from one to five years	121,180
Due from five to ten years	251,643
Due after ten years	27,861
Total securities available for sale	429,669
Fair Value [Abstract]
Due in one year or less	29,472
Due from one to five years	127,163
Due from five to ten years	247,017
Due after ten years	26,191
Total securities available for sale	429,843	402,353
Amortized Cost [Abstract]
Due in one year or less	837
Due from one to five years	6,262
Due from five to ten years	265
Total securities held to maturity	7,364
Total investment securities	437,033
Fair Value [Abstract]
Due in one year or less	854
Due from one to five years	6,889
Due from five to ten years	281
Total securities held to maturity	8,024
Total investment securities	$ 437,867