Consolidated Statements of Changes in Shareholders' Equity (Parenthetical) - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Proceeds from exercise of options, shares 0 5,000 0 5,000
Cash dividends, per share $ 0.4125 $ 0.4075 $ 0.4125 $ 0.4075
Common Stock [Member]        
Issuance of shares of common stock to the ESPP     2,418