Regulatory Matters (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Tier 1 Capital (to average assets)
Amount available without prior regulatory approval for dividends	$ 117,700
Company
Total Capital (to risk-weighted assets)
Total Capital (to risk-weighted assets), Actual, Capital Amount	$ 637,472	$ 393,654
Total Capital (to risk weighted assets), Actual, Ratio (as a percent)	11.60%	12.30%
Total Capital, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 440,063	$ 255,884
Total Capital (to risk weighted assets), Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	8.00%	8.00%
Tier I Capital (to risk-weighted assets)
Tier I Capital, (to risk-weighted assets), Actual, Capital Amount	$ 621,630	$ 380,950
Tier I Capital (to risk weighted assets), Actual, Ratio (as a percent)	11.30%	11.90%
Tier I Capital, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 330,047	$ 191,913
Tier I Capital (to risk weighted assets), Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	6.00%	6.00%
Common Equity Tier I Capital 1 (to risk-weighted assets)
Common Equity Tier I Capital 1, Actual, Capital Amount	$ 408,984	$ 339,369
Common Equity Tier I Capital 1 (to risk weighted assets), Ratio (as a percent)	7.40%	10.60%
Common Equity Tier I Capital 1, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 247,536	$ 143,935
Common Equity Tier I Capital 1 (to risk weighted assets, Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	4.50%	4.50%
Tier 1 Capital (to average assets)
Tier 1 Capital, Actual, Capital Amount	$ 621,630	$ 380,950
Tier 1 Capital (to average assets), Actual, Ratio (as a percent)	9.40%	10.00%
Tier 1 Capital, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 264,324	$ 152,081
Tier 1 Capital (to average assets), Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	4.00%	4.00%
Federal Deposit Corporation And Federal Reserve Board | Rules Effective January 1, 2015
Tier 1 Capital (to average assets)
Basel III Capital Rules related to CET1, period (in years)	4 years
Additional capital conservation buffer requirement subsequent years Ratio	2.50%
Merchants Bank
Total Capital (to risk-weighted assets)
Total Capital (to risk-weighted assets), Actual, Capital Amount	$ 639,104	$ 412,386
Total Capital (to risk weighted assets), Actual, Ratio (as a percent)	12.00%	13.30%
Total Capital, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 426,748	$ 248,290
Total Capital (to risk weighted assets), Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	8.00%	8.00%
Total capital, Minimum Amount To Be Well Capitalized, Capital Amount	$ 533,435	$ 310,363
Total Capital (to risk weighted assets), Minimum Amount To Be Well Capitalized, Ratio (as a percent)	10.00%	10.00%
Tier I Capital (to risk-weighted assets)
Tier I Capital, (to risk-weighted assets), Actual, Capital Amount	$ 623,716	$ 399,815
Tier I Capital (to risk weighted assets), Actual, Ratio (as a percent)	11.70%	12.90%
Tier I Capital, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 320,061	$ 186,218
Tier I Capital (to risk weighted assets), Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	6.00%	6.00%
Tier I Capital, Minimum Amount To Be Well Capitalized, Capital Amount	$ 426,748	$ 248,290
Tier I Capital (to risk weighted assets), Minimum Amount To Be Well Capitalized, Ratio (as a percent)	8.00%	8.00%
Common Equity Tier I Capital 1 (to risk-weighted assets)
Common Equity Tier I Capital 1, Actual, Capital Amount	$ 623,716	$ 399,815
Common Equity Tier I Capital 1 (to risk weighted assets), Ratio (as a percent)	11.70%	12.90%
Common Equity Tier I Capital 1, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 240,046	$ 139,663
Common Equity Tier I Capital 1 (to risk weighted assets, Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	4.50%	4.50%
Common Equity Tier I Capital 1, Minimum Amount To Be Well Capitalized, Capital Amount	$ 346,733	$ 201,736
Common Equity Tier I Capital 1 (to risk weighted assets), Minimum Amount To Be Well Capitalized, Ratio (as a percent)	6.50%	6.50%
Tier 1 Capital (to average assets)
Tier 1 Capital, Actual, Capital Amount	$ 623,716	$ 399,815
Tier 1 Capital (to average assets), Actual, Ratio (as a percent)	9.70%	11.00%
Tier 1 Capital, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 257,487	$ 145,723
Tier 1 Capital (to average assets), Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	4.00%	4.00%
Tier 1 Capital, Minimum Amount To Be Well Capitalized, Capital Amount	$ 321,859	$ 182,154
Tier 1 Capital (to average assets), Minimum Amount To Be Well Capitalized, Ratio (as a percent)	5.00%	5.00%
FMBI
Total Capital (to risk-weighted assets)
Total Capital (to risk-weighted assets), Actual, Capital Amount	$ 21,726	$ 17,537
Total Capital (to risk weighted assets), Actual, Ratio (as a percent)	13.10%	18.60%
Total Capital, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 13,306	$ 7,559
Total Capital (to risk weighted assets), Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	8.00%	8.00%
Total capital, Minimum Amount To Be Well Capitalized, Capital Amount	$ 16,632	$ 9,448
Total Capital (to risk weighted assets), Minimum Amount To Be Well Capitalized, Ratio (as a percent)	10.00%	10.00%
Tier I Capital (to risk-weighted assets)
Tier I Capital, (to risk-weighted assets), Actual, Capital Amount	$ 21,272	$ 17,404
Tier I Capital (to risk weighted assets), Actual, Ratio (as a percent)	12.80%	18.40%
Tier I Capital, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 9,979	$ 5,669
Tier I Capital (to risk weighted assets), Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	6.00%	6.00%
Tier I Capital, Minimum Amount To Be Well Capitalized, Capital Amount	$ 13,306	$ 7,559
Tier I Capital (to risk weighted assets), Minimum Amount To Be Well Capitalized, Ratio (as a percent)	8.00%	8.00%
Common Equity Tier I Capital 1 (to risk-weighted assets)
Common Equity Tier I Capital 1, Actual, Capital Amount	$ 21,272	$ 17,404
Common Equity Tier I Capital 1 (to risk weighted assets), Ratio (as a percent)	12.80%	18.40%
Common Equity Tier I Capital 1, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 7,484	$ 4,252
Common Equity Tier I Capital 1 (to risk weighted assets, Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	4.50%	4.50%
Common Equity Tier I Capital 1, Minimum Amount To Be Well Capitalized, Capital Amount	$ 10,811	$ 6,141
Common Equity Tier I Capital 1 (to risk weighted assets), Minimum Amount To Be Well Capitalized, Ratio (as a percent)	6.50%	6.50%
Tier 1 Capital (to average assets)
Tier 1 Capital, Actual, Capital Amount	$ 21,272	$ 17,404
Tier 1 Capital (to average assets), Actual, Ratio (as a percent)	11.70%	10.80%
Tier 1 Capital, Minimum Amount Required for Adequately Capitalized, Capital Amount	$ 7,302	$ 6,453
Tier 1 Capital (to average assets), Minimum Amount Required for Adequately Capitalized, Ratio (as a percent)	4.00%	4.00%
Tier 1 Capital, Minimum Amount To Be Well Capitalized, Capital Amount	$ 9,128	$ 8,066
Tier 1 Capital (to average assets), Minimum Amount To Be Well Capitalized, Ratio (as a percent)	5.00%	5.00%