Regulatory Matters (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Total Capital (to Risk-Weighted Assets):
Actual Amount		$ 882,453	$ 821,975
Actual Ratio (as a percent)		14.90%	14.68%
Minimum Capital Adequacy Amount		$ 473,782	$ 447,909
Minimum Capital Adequacy Ratio (as a percent)		8.00%	8.00%
Capital Required For Capital Adequacy With Capital Buffer		$ 621,839	$ 552,888
Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets	[1]	10.50%	9.875%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 592,227	$ 559,887
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		$ 807,926	$ 751,575
Actual Ratio (as a percent)		13.64%	13.42%
Minimum Capital Adequacy Amount		$ 355,336	$ 335,932
Minimum Capital Adequacy Ratio (as a percent)		6.00%	6.00%
Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer		$ 503,393	$ 440,911
Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets	[1]	8.50%	7.875%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 473,782	$ 447,909
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		$ 743,467	$ 693,067
Actual Ratio (as a percent)		12.55%	12.38%
Minimum Capital Adequacy Amount		$ 266,502	$ 251,949
Minimum Capital Adequacy Ratio (as a percent)		4.50%	4.50%
Common Equity Tier 1 Capita Required Form Minimum Capital Adequacy With Capital Buffer		$ 414,559	$ 356,928
Common Equity Tier 1 Capital Required For Capital Adequacy With Capital Buffer to Risk Weighted Assets	[1]	7.00%	6.375%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 384,948	$ 363,926
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		$ 807,926	$ 751,575
Actual Ratio (as a percent)		12.19%	12.06%
Minimum Capital Adequacy Amount		$ 265,122	$ 249,185
Minimum Capital Adequacy Ratio (as a percent)		4.00%	4.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 331,402	$ 311,481
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		$ 804,131	$ 744,326
Actual Ratio (as a percent)		13.57%	13.29%
Minimum Capital Adequacy Amount		$ 474,189	$ 448,152
Minimum Capital Adequacy Ratio (as a percent)		8.00%	8.00%
Capital Required For Capital Adequacy With Capital Buffer		$ 622,373	$ 553,188
Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets	[1]	10.50%	9.875%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 592,736	$ 560,190
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		$ 729,541	$ 673,888
Actual Ratio (as a percent)		12.31%	12.03%
Minimum Capital Adequacy Amount		$ 355,642	$ 336,114
Minimum Capital Adequacy Ratio (as a percent)		6.00%	6.00%
Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer		$ 503,826	$ 441,150
Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets	[1]	8.50%	7.875%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 474,189	$ 448,152
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		$ 722,082	$ 672,380
Actual Ratio (as a percent)		12.18%	12.00%
Minimum Capital Adequacy Amount		$ 266,731	$ 252,086
Minimum Capital Adequacy Ratio (as a percent)		4.50%	4.50%
Common Equity Tier 1 Capita Required Form Minimum Capital Adequacy With Capital Buffer		$ 414,915	$ 357,121
Common Equity Tier 1 Capital Required For Capital Adequacy With Capital Buffer to Risk Weighted Assets	[1]	7.00%	6.375%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 385,279	$ 364,124
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		$ 729,541	$ 673,888
Actual Ratio (as a percent)		11.03%	10.82%
Minimum Capital Adequacy Amount		$ 264,500	$ 249,052
Minimum Capital Adequacy Ratio (as a percent)		4.00%	4.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		$ 330,625	$ 311,315
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		5.00%	5.00%

[1] (1) The capital conservation buffer requirement was fully phased in as of December 31, 2019.