Retirement Plans (Tables)

12 Months Ended

Dec. 31, 2012

Compensation and Retirement Disclosure [Abstract]

Schedule of Changes in the Projected Benefit Obligation and Plan Assets of the Corporation’s Pension and Postretirement Plans

The following schedule sets forth the changes in the projected benefit obligation and plan assets of the Corporation's Pension and Postretirement Plans:

	Pension Plan						Postretirement Plan
	2012			2011			2012			2011
	(In thousands)
Projected benefit obligation:
Benefit obligation at beginning of year	$	100,216		$	86,704		$	3,290		$	3,757
Service cost	1,168			1,133			—			—
Interest cost	4,795			4,779			146			167
Net actuarial (gain) loss	13,200			11,082			25			(490		)
Benefits paid	(4,202		)	(3,482		)	(218		)	(144		)
Benefit obligation at end of year	115,177			100,216			3,243			3,290
Fair value of plan assets:
Fair value of plan assets at beginning of year	82,521			86,741			—			—
Actual return on plan assets	7,868			(738		)	—			—
Employer contributions	12,000			—			218			144
Benefits paid	(4,202		)	(3,482		)	(218		)	(144		)
Fair value of plan assets at end of year	98,187			82,521			—			—
Unfunded projected benefit obligation at December 31	$	16,990		$	17,695		$	3,243		$	3,290
Accumulated benefit obligation	$	108,078		$	94,089		$	3,243		$	3,290

Schedule of Weighted-average rate assumptions of the Pension and Postretirement Plans

Weighted-average rate assumptions of the Pension and Postretirement Plans follow:

	Pension Plan						Postretirement Plan
	2012		2011		2010		2012		2011		2010
Discount rate used in determining benefit obligation — December 31	4.08	%	4.90	%	5.65	%	4.08	%	4.90	%	5.65	%
Discount rate used in determining expense	4.90		5.65		6.15		4.90		5.65		6.15
Expected long-term return on Pension Plan assets	7.00		7.00		7.00		—		—		—
Rate of compensation increase used in determining benefit obligation — December 31	3.50		3.50		3.50		—		—		—
Rate of compensation increase used in determining pension expense	3.50		3.50		3.50		—		—		—
Year 1 increase in cost of postretirement benefits	—		—		—		8.0		9.0		9.0

Schedule of Net periodic Pension Cost (Income) of the Pension and Postretirement Plans

Net periodic pension cost (income) of the Pension and Postretirement Plans was as follows for the years ended December 31:

	Pension Plan									Postretirement Plan
	2012			2011			2010			2012			2011			2010
	(In thousands)
Service cost	$	1,168		$	1,133		$	1,228		$	—		$	—		$	—
Interest cost	4,795			4,779			4,785			146			167			217
Expected return on plan assets	(6,925		)	(6,328		)	(5,724		)	—			—			—
Amortization of prior service credit	(1		)	(2		)	(2		)	(300		)	(325		)	(324		)
Amortization of net actuarial loss (gain)	2,382			1,073			491			(28		)	(31		)	—
Net cost (income)	$	1,419		$	655		$	778		$	(182	)	$	(189	)	$	(107	)

Schedule of Estimated Future Benefit Payments Under the Pension and Postretirement Plans

The following schedule presents estimated future benefit payments under the Pension and Postretirement Plans for retirees already receiving benefits and future retirees, assuming they retire and begin receiving unreduced benefits as soon as they are eligible:

	Pension Plan		Postretirement Plan
	(In thousands)
2013	$	4,708	$	272
2014	4,998		275
2015	5,380		275
2016	6,019		269
2017	5,989		260
2018 - 2022	32,507		1,171
Total	$	59,601	$	2,522

Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates

A one percentage-point change in these rates would have the following effects:

	One Percentage-Point
	Increase		Decrease
	(In thousands)
Effect on total of service and interest cost components in 2012	$	11	$	(10	)
Effect on postretirement benefit obligation as of December 31, 2012	262		(233		)

Schedule of Allocation of Plan Assets

The following schedule sets forth the fair value of the Pension Plan's assets and the level of the valuation inputs used to value those assets at December 31, 2012 and 2011:

Asset Category	Quoted Prices In Active Markets  for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
	(In thousands)
December 31, 2012
Cash	$	1,708	$	—	$	—	$	1,708
Equity securities:
U.S. large- and mid-cap stocks(a)	44,158		—		—		44,158
U.S. small-cap mutual funds	4,076		—		—		4,076
International large-cap mutual funds	9,009		—		—		9,009
Emerging markets mutual funds	6,291		—		—		6,291
Chemical Financial Corporation common stock	5,005		—		—		5,005
Debt securities:
U.S. Treasury and government sponsored agency bonds and notes	4,876		1,056		—		5,932
Corporate bonds(b)	—		15,853		—		15,853
Mutual funds(c)	6,005		—		—		6,005
Other	150		—		—		150
Total	$	81,278	$	16,909	$	—	$	98,187
December 31, 2011
Cash	$	1,773	$	—	$	—	$	1,773
Equity securities:
U.S. large- and mid-cap stocks(a)	35,503		—		—		35,503
U.S. small-cap mutual funds	3,303		—		—		3,303
International large-cap mutual funds	10,659		—		—		10,659
Emerging markets mutual funds	3,954		—		—		3,954
Chemical Financial Corporation common stock	4,726		—		—		4,726
Debt securities:
U.S. Treasury and government sponsored agency bonds and notes	5,717		2,053		—		7,770
Corporate bonds(b)	—		14,603		—		14,603
Other	230		—		—		230
Total	$	65,865	$	16,656	$	—	$	82,521

(a) Comprised of common stocks traded on U.S. Exchanges whose issuers had market capitalizations exceeding $3 billion.

(b) Comprised of investment grade bonds of U.S. issuers from diverse industries.

(c) Comprised primarily of fixed-income bonds issued by the U.S. Treasury and government sponsored agencies and bonds of U.S. and foreign issuers from diverse industries.

The Pension Plan's asset allocation by asset category was as follows:

	December 31,
Asset Category	2012		2011
Equity securities	70	%	71	%
Debt securities	28		27
Other	2		2
Total	100	%	100	%

Schedule of Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax, Related to the Corporation’s Pension, Postretirement and Supplemental Plans

The following sets forth the changes in accumulated other comprehensive income (loss), net of tax, related to the Corporation's Pension, Postretirement and Supplemental Plans during 2012:

	Pension Plan			Postretirement Plan			Supplemental Plan			Total
	(In thousands)
Accumulated other comprehensive income (loss) at beginning of year	$	(28,869	)	$	513		$	(309	)	$	(28,665	)
Comprehensive income (loss) adjustment:
Prior service credits	(1		)	(195		)	—			(196		)
Net actuarial gain (loss)	(6,418		)	(35		)	(79		)	(6,532		)
Comprehensive income (loss) adjustment	(6,419		)	(230		)	(79		)	(6,728		)
Accumulated other comprehensive income (loss) at end of year	$	(35,288	)	$	283		$	(388	)	$	(35,393	)

Schedule of Estimated Income (Loss) That Will Be Amortized From Accumulated Other Comprehensive Income (Loss) Into Net Periodic Cost

The estimated income (loss) that will be amortized from accumulated other comprehensive income (loss) into net periodic cost, net of tax, in 2013 is as follows:

	Pension Plan			Postretirement Plan		Supplemental Plan			Total
	(In thousands)
Prior service credits	$	1		$	—	$	—		$	1
Net gain (loss)	(2,385		)	6		(75		)	(2,454		)
Total	$	(2,384	)	$	6	$	(75	)	$	(2,453	)