Segments (Details) (USD $)	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Selected financial information by business segment
Net interest income	$ 18,310,000	$ 18,795,000	$ 18,295,000	$ 18,550,000	$ 18,016,000	$ 17,790,000	$ 17,611,000	$ 17,315,000	$ 17,324,000	$ 17,214,000	$ 16,547,000	$ 15,794,000	$ 73,950,000	$ 70,732,000	$ 66,879,000
Provision for loan losses	2,475,000	2,475,000	2,475,000	4,075,000	3,100,000	4,100,000	2,600,000	2,800,000	3,695,000	2,695,000	2,384,000	2,695,000	11,500,000	12,600,000	11,469,000
Investment management and trust services													14,278,000	13,841,000	13,260,000
All other non-interest income													24,179,000	19,403,000	20,479,000
Non-interest expense	17,183,000	17,045,000	16,508,000	14,736,000	16,727,000	13,302,000	14,725,000	14,827,000	15,083,000	13,909,000	14,381,000	13,758,000	65,472,000	59,581,000	57,131,000
Income before income taxes	8,779,000	9,070,000	8,602,000	8,984,000	7,418,000	8,246,000	8,438,000	7,693,000	8,124,000	8,872,000	7,705,000	7,317,000	35,435,000	31,795,000	32,018,000
Tax expense	2,265,000	2,388,000	2,499,000	2,482,000	1,076,000	2,472,000	2,441,000	2,202,000	2,073,000	2,507,000	2,149,000	2,336,000	9,634,000	8,191,000	9,065,000
Net income	6,514,000	6,682,000	6,103,000	6,502,000	6,342,000	5,774,000	5,997,000	5,491,000	6,051,000	6,365,000	5,556,000	4,981,000	25,801,000	23,604,000	22,953,000
Goodwill related to the 1996 purchase of a bank in southern Indiana	682,000				682,000								682,000	682,000
Commercial banking
Selected financial information by business segment
Net interest income													73,800,000	70,592,000	66,764,000
Provision for loan losses													11,500,000	12,600,000	11,469,000
All other non-interest income													24,110,000	19,382,000	20,479,000
Non-interest expense													57,323,000	51,863,000	49,618,000
Income before income taxes													29,087,000	25,511,000	26,156,000
Tax expense													7,412,000	5,992,000	7,013,000
Net income													21,675,000	19,519,000	19,143,000
Goodwill related to the 1996 purchase of a bank in southern Indiana	682,000												682,000
Investment management and trust
Selected financial information by business segment
Net interest income													150,000	140,000	115,000
Investment management and trust services													14,278,000	13,841,000	13,260,000
All other non-interest income													69,000	21,000
Non-interest expense													8,149,000	7,718,000	7,513,000
Income before income taxes													6,348,000	6,284,000	5,862,000
Tax expense													2,222,000	2,199,000	2,052,000
Net income													$ 4,126,000	$ 4,085,000	$ 3,810,000