Consolidated Statements of Changes in Shareholders' Equity [Parenthetical] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Stock option exercises (in shares)	155,769	43,801	29,975
Issuance of restricted common stock (in shares)	4,549	6,205	7,500
Cash dividends (in usd per share)	$ 0.60	$ 0.60	$ 0.58
Dividend reinvestment plan shares issued from reserve (in shares)	221,506	41,485	37,707
Issuance of common stock (in shares)	9,516,097