Investment Securities, Amortized Cost, Maturities and Approximate Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Amortized Cost [Abstract]
Due in one year or less	$ 42,434
Due from one to five years	116,217
Due from five to ten years	209,792
Due after ten years	30,178
Total securities available for sale	398,621
Fair Value [Abstract]
Due in one year or less	43,232
Due from one to five years	123,531
Due from five to ten years	216,357
Due after ten years	30,157
Total securities available for sale	413,277	402,353
Amortized Cost [Abstract]
Due in one year or less	1,535
Due from one to five years	5,938
Due from five to ten years	398
Total securities held to maturity	7,871
Total investment securities	406,492
Fair Value [Abstract]
Due in one year or less	1,545
Due from one to five years	6,672
Due from five to ten years	445
Total securities held to maturity	8,662
Total investment securities	$ 421,939