Retirement Plans (Textual) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) employee shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Common Stock, Shares Held by Plan | shares	71,460,119	71,207,114
Dividends paid (in dollars per share)	$ 88,954	$ 78,498	$ 49,389
Multiemployer Plan, Contributions by Employer	0
Multiemployer Plan, Participating Company, Allocation of Plan Liabilities	$ 3,800	3,700
Multiemployer Plan, Company's Asset Participation Level	0.10%
Employer discretionary contribution percent	4.00%
Employer total contribution amount	$ 8,400	$ 9,100	$ 6,500
Maximum annual contribution per employee percent	50.00%
Employer matching contribution percent	4.00%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate used in determining benefit obligation	4.32%	3.68%	4.22%
Number of Employees Covered (in employee) | employee	80
Pension Plan expense	$ (3,813)	$ (1,495)	$ 73
Employer contributions	$ 0	$ 0
Discount rate used in determining expense	3.68%	4.22%	4.55%
Curtailment	$ 0	$ 11,911
Pension plan actual asset allocations	100.00%	100.00%
Projected benefit obligation	$ 111,432	$ 121,361	$ 123,968
Accumulated benefit obligation	111,432	121,361
Settlement	$ 0	$ 0	$ 0
Pension Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan actual asset allocations	67.00%	68.00%
Pension Plan | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan actual asset allocations	26.00%	28.00%
Pension Plan | Other
Defined Benefit Plan Disclosure [Line Items]
Pension plan actual asset allocations	7.00%	4.00%
Pension Plan | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Common Stock, Shares Held by Plan | shares		0
SERP
Defined Benefit Plan Disclosure [Line Items]
Discount rate used in determining benefit obligation	4.32%	3.38%	3.63%
Pension Plan expense	$ 5	$ 529	$ 367
Employer contributions	$ 0	$ 0
Discount rate used in determining expense	0.00%	0.00%	4.51%
Curtailment	$ 0	$ 0
Number of employees covered by the pension plan | employee	1
Projected benefit obligation	$ 337	2,423	$ 2,567
Accumulated benefit obligation	337	2,423
Settlement	$ 0	$ (322)	$ (120)
Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate used in determining benefit obligation	4.11%	3.41%	3.79%
Pension Plan expense	$ (58)	$ (63)	$ 158
Employer contributions	$ 0	$ 198
Discount rate used in determining expense	3.41%	3.79%	4.23%
Curtailment	$ 0	$ 0
Expected health care cost trend rate assumed for 2014	7.50%
Expected ultimate health care cost trend rate in 2020	5.00%
Projected benefit obligation	$ 2,200	2,512	$ 2,601
Accumulated benefit obligation	2,200	2,512
Settlement	$ 0	0	$ 0
Minimum retirement age (years)	50 years
Maximum benefit age of spouse (years)	65 years
Minimum retirement age with twenty-five years of service to be eligible for postretirement benefits (years)	60 years
Minimum years of service for retirees at age sixty to be eligible for postretirement benefits (years)	25 years
Chemical Financial Corporation | Pension Plan | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Dividends paid (in dollars per share)		$ 200
Minimum | Pension Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range	40.00%
Minimum | Pension Plan | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range	20.00%
Minimum | Pension Plan | Other
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range	0.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Employer discretionary contribution percent	6.00%
Maximum | Pension Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range	70.00%
Maximum | Pension Plan | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range	60.00%
Maximum | Pension Plan | Other
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range	10.00%
Nonqualified Plan | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefits owed related to change in control	$ 300