Investment Securities, Amortized Cost, Maturities and Approximate Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Amortized Cost [Abstract]
Due in one year or less	$ 18,003
Due from one to five years	123,574
Due from five to ten years	251,818
Due after ten years	22,850
Total securities available for sale	416,245
Fair Value [Abstract]
Due in one year or less	18,252
Due from one to five years	129,476
Due from five to ten years	245,440
Due after ten years	20,983
Total securities available for sale	414,151	402,353
Amortized Cost [Abstract]
Due in one year or less	777
Due from one to five years	6,168
Due from five to ten years	205
Total securities held to maturity	7,150
Total investment securities	423,395
Fair Value [Abstract]
Due in one year or less	790
Due from one to five years	6,784
Due from five to ten years	219
Total securities held to maturity	7,793
Total investment securities	$ 421,944