Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Scheduled maturities of securities
Weighted Average Yield, Due in one year or less	0.0371	0.0380
Amortized cost, Due in one year or less	$ 22,982	$ 19,137
Fair value, Due in one year or less	23,303	19,411
Weighted Average Yield, Due from one year to five years	0.0306	0.0305
Amortized cost, Due from one year to five years	187,547	187,595
Fair value, Due from one year to five years	195,987	195,182
Weighted Average Yield, Due from five to ten years	0.0315	0.0327
Amortized cost, Due from five to ten years	106,489	108,288
Fair value, Due from five to ten years	110,108	111,879
Weighted Average Yield, Due after ten years	0.0318	0.0330
Amortized cost, Due after ten years	727,065	749,285
Fair value, Due after ten years	755,240	782,486
Weighted Average Yield, Total	0.0317	0.0326
Amortized cost, Total	1,044,083	1,064,305
Fair value, Total	$ 1,084,638	$ 1,108,958