Regulatory Matters (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Total Capital (to Risk-Weighted Assets):
Actual Amount		$ 713,498	$ 676,007
Actual Ratio (as a percent)		15.12%	14.97%
Minimum Capital Adequacy Amount		$ 377,432	$ 361,267
Minimum Capital Adequacy Ratio (as a percent)		8.00%	8.00%
Capital Required For Capital Adequacy With Capital Buffer		$ 406,919
Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets	[1]	8.625%
Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets Fully Phased In		10.50%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 471,791	$ 451,584
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		10.00%	10.00%
Tier I Capital (to Risk-Weighted Assets):
Actual Amount		$ 651,006	$ 616,577
Actual Ratio (as a percent)		13.80%	13.65%
Minimum Capital Adequacy Amount		$ 283,074	$ 270,951
Minimum Capital Adequacy Ratio (as a percent)		6.00%	6.00%
Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer		$ 312,561
Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets	[1]	6.625%
Tier One Risk Based Capital Required For Capital Adequacy With Capital Buffer To Risk Weighted Assets Fully Phased In		8.50%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 377,432	$ 361,267
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		8.00%	8.00%
Common Equity Tier 1 Capital (to Risk-Weighted Assets):
Actual Amount		$ 594,006	$ 559,577
Actual Ratio (as a percent)		12.59%	12.39%
Minimum Capital Adequacy Amount		$ 212,306	$ 203,213
Minimum Capital Adequacy Ratio (as a percent)		4.50%	4.50%
Common Equity Tier 1 Capita Required Form Minimum Capital Adequacy With Capital Buffer		$ 241,793
Common Equity Tier 1 Capital Required For Capital Adequacy With Capital Buffer to Risk Weighted Assets	[1]	5.125%
Common Equity Tier 1 Capital Required For Capital Adequacy With Capital Buffer to Risk Weighted Assets Fully Phased In		7.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 306,664	$ 293,530
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		6.50%	6.50%
Tier I Capital (to Average Assets):
Actual Amount		$ 651,006	$ 616,577
Actual Ratio (as a percent)		12.11%	12.21%
Minimum Capital Adequacy Amount		$ 215,115	$ 201,921
Minimum Capital Adequacy Ratio (as a percent)		4.00%	4.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 268,893	$ 252,401
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		5.00%	5.00%
1st Source Bank
Total Capital (to Risk-Weighted Assets):
Actual Amount		$ 662,531	$ 636,592
Actual Ratio (as a percent)		14.06%	14.13%
Minimum Capital Adequacy Amount		$ 377,014	$ 360,402
Minimum Capital Adequacy Ratio (as a percent)		8.00%	8.00%
Capital Required For Capital Adequacy With Capital Buffer		$ 406,468
Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets	[1]	8.625%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 471,267	$ 450,502
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		10.00%	10.00%
Tier I Capital (to Risk-Weighted Assets):
Actual Amount		$ 603,022	$ 579,833
Actual Ratio (as a percent)		12.80%	12.87%
Minimum Capital Adequacy Amount		$ 282,760	$ 270,301
Minimum Capital Adequacy Ratio (as a percent)		6.00%	6.00%
Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer		$ 312,214
Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets	[1]	6.625%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 377,014	$ 360,402
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		8.00%	8.00%
Common Equity Tier 1 Capital (to Risk-Weighted Assets):
Actual Amount		$ 603,022	$ 579,833
Actual Ratio (as a percent)		12.80%	12.87%
Minimum Capital Adequacy Amount		$ 212,070	$ 202,726
Minimum Capital Adequacy Ratio (as a percent)		4.50%	4.50%
Common Equity Tier 1 Capita Required Form Minimum Capital Adequacy With Capital Buffer		$ 241,524
Common Equity Tier 1 Capital Required For Capital Adequacy With Capital Buffer to Risk Weighted Assets	[1]	5.125%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 306,324	$ 292,826
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		6.50%	6.50%
Tier I Capital (to Average Assets):
Actual Amount		$ 603,022	$ 579,833
Actual Ratio (as a percent)		11.22%	11.50%
Minimum Capital Adequacy Amount		$ 214,949	$ 201,701
Minimum Capital Adequacy Ratio (as a percent)		4.00%	4.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 268,686	$ 252,126
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		5.00%	5.00%

[1] (1) The capital conservation buffer requirement will be phased in over three years beginning in 2016. The capital buffer requirement effectively raises the minimum required common equity Tier 1 capital ratio to 7.0%, the Tier 1 capital ratio to 8.5%, and the total capital ratio to 10.5% on a fully phased-in basis.