Retirement Plans (Textual) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 24, 2014	Sep. 18, 2013
Defined Benefit Plan Disclosure [Line Items]
Percentage of eligible pay contribution to certain employees	4.00%
Common Stock, Shares Held by Plan	(32,774,420)	(29,789,825)		(2,500,000)	(2,213,750)
Dividends paid	$ 29,528,000	$ 24,521,000	$ 22,566,000
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum years of vested service for calculation of retirement benefits	30 years
Years of employees highest average salary for calculation of retirement benefits	5 years
Defined Benefit Plan, Number of Employees Covered	179
Number of years preceding retirement for calculation of retirement benefits	10 years
Maximum years of service for which pension benefits calculation is based upon vested service and average five years of salary	15 years
Maximum total years of age and years of service for which pension benefits calculation is based upon vested service and average five years of salary	65 years
Pension Plan expense	(45,000)	1,725,000	1,419,000
Employer contributions	0	15,000,000	12,000,000
Discount rate used in determining benefit obligation	4.15%	5.00%	4.08%
Pension plan actual asset allocations	100.00%	100.00%
Projected benefit obligation	129,160,000	105,914,000	115,177,000
Accumulated benefit obligation	121,826,000	99,551,000
Pension Plan [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range - minimum	60.00%
Target plan asset allocations range - maximum	70.00%
Pension plan actual asset allocations	68.00%	70.00%
Pension Plan [Member] | Debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range - minimum	30.00%
Target plan asset allocations range - maximum	40.00%
Pension plan actual asset allocations	30.00%	29.00%
Pension Plan [Member] | Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range - minimum	0.00%
Target plan asset allocations range - maximum	10.00%
Pension plan actual asset allocations	2.00%	1.00%
Pension Plan [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Common Stock, Shares Held by Plan	(210,663)
Fair value of common stock	6,500,000	6,700,000
Pension plan actual asset allocations	4.90%	5.20%
Supplemental Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of employees covered by the pension plan	1
Discount rate used in determining benefit obligation	4.07%	4.87%	4.08%
Projected benefit obligation	2,100,000	1,700,000
Accumulated benefit obligation	2,000,000	1,500,000
Supplemental Plan expense	300,000	200,000	200,000
Postretirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension Plan expense	186,000	431,000	(182,000)
Employer contributions	247,000	219,000
Discount rate used in determining benefit obligation	3.75%	4.27%	4.08%
Expected health care cost trend rate assumed for 2014	8.00%
Expected ultimate health care cost trend rate in 2020	5.00%
Projected benefit obligation	3,702,000	3,477,000	3,243,000
Accumulated benefit obligation	3,702,000	3,477,000
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 [Member] | Pension Plan [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Dividends paid	$ 200,000	$ 180,000