Regulatory Capital (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (to Risk-weighted Assets), Actual Amount	$ 599,966	$ 526,792
Total Capital (to Risk-weighted Assets) Actual Ratio	14.54%	16.34%
Total Capital (to Risk-weighted Assets) Required for Adequate Capital, Amount	330,107	257,927
Total Capital (to Risk-weighted Assets) Required for Adequate Capital, Ratio	8.00%	8.00%
Tier I Capital (to Risk-weighted Assets), Actual Amount	483,186	456,132
Tier I Capital (to Risk-weighted Assets), Ratio	11.71%	14.15%
Tier I Capital (to Risk-weighted Assets) Required for Adequate Capital, Amount	165,053	128,964
Tier I Capital (to Risk-weighted Assets) Required for Adequate Capital, Ratio	4.00%	4.00%
Tier I Capital (to Average Assets), Actual	483,186	456,132
Tier I Capital (to Average Assets), Ratio	10.20%	11.03%
Tier I Capital (to Average Assets) Required for Adequate Capital, Amount	189,485	165,460
Tier I Capital (to Average Assets) Required for Adequate Capital, Ratio	4.00%	4.00%
First Merchants Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (to Risk-weighted Assets) Well Capitalized Ratio	10.00%
Tier I Capital (to Risk-weighted Assets) Well Capitalized Ratio	6.00%
Tier I Capital (to Average Assets) Well Capitalized Ratio	5.00%
Total Capital (to Risk-weighted Assets), Actual Amount	599,272	515,337
Total Capital (to Risk-weighted Assets) Actual Ratio	14.56%	16.01%
Total Capital (to Risk-weighted Assets) Required for Adequate Capital, Amount	329,344	257,446
Total Capital (to Risk-weighted Assets) Required for Adequate Capital, Ratio	8.00%	8.00%
Tier I Capital (to Risk-weighted Assets), Actual Amount	547,655	474,782
Tier I Capital (to Risk-weighted Assets), Ratio	13.30%	14.75%
Tier I Capital (to Risk-weighted Assets) Required for Adequate Capital, Amount	164,672	128,723
Tier I Capital (to Risk-weighted Assets) Required for Adequate Capital, Ratio	4.00%	4.00%
Tier I Capital (to Average Assets), Actual	547,655	474,782
Tier I Capital (to Average Assets), Ratio	11.58%	11.50%
Tier I Capital (to Average Assets) Required for Adequate Capital, Amount	$ 189,095	$ 165,124
Tier I Capital (to Average Assets) Required for Adequate Capital, Ratio	4.00%	4.00%