Securities Sold Under Agreements to Repurchase (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Federal Funds Purchased and Securities Sold Under Agreements to Repurchase    
Maximum maturity period of securities sold under agreements to repurchase 1 year  
Balance $ 198,893 $ 172,348
Weighted average interest rate at end of period (as a percent) 0.14% 0.13%
Maximum outstanding at any month end 198,893 172,348
Average daily balance $ 148,452 $ 137,777
Weighted average interest rate during period (as a percent) 0.12% 0.14%