TCF Financial 10-Q 31 Oct 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 18, 2013
Entity Information [Line Items]	'	'
Entity Registrant Name	'CHEMICAL FINANCIAL CORP	'
Entity Central Index Key	'0000019612	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-13	'
Amendment Flag	'false	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	29,778,250

Consolidated_Statements_of_Fin

Consolidated Statements of Financial Position (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Cash and cash equivalents:	'	'	'
Cash and cash due from banks	$135,839	$142,467	$123,519
Interest-bearing deposits with the Federal Reserve Bank	357,271	513,668	315,201
Total cash and cash equivalents	493,110	656,135	438,720
Investment securities:	'	'	'
Available-for-sale, at fair value	705,146	586,809	646,578
Held-to-maturity (fair value - $275,866 at September 30, 2013, $229,922 at December 31, 2012 and $223,185 at September 30, 2012)	282,579	229,977	221,536
Total investment securities	987,725	816,786	868,114
Loans held-for-sale	'	17,665	15,075
Loans	4,522,671	4,167,735	4,019,159
Allowance for loan losses	-81,532	-84,491	-84,694
Net loans	4,441,139	4,083,244	3,934,465
Premises and equipment (net of accumulated depreciation of $98,150 at September 30, 2013, $93,207 at December 31, 2012 and $91,203 at September 30, 2012)	73,690	75,458	67,796
Goodwill	120,164	120,164	113,414
Other intangible assets	13,865	15,388	10,243
Interest receivable and other assets	120,636	132,412	132,594
Total Assets	6,258,236	5,917,252	5,580,421
Deposits:	'	'	'
Noninterest-bearing	1,162,599	1,085,857	952,126
Interest-bearing	4,028,706	3,835,586	3,646,746
Total deposits	5,191,305	4,921,443	4,598,872
Interest payable and other liabilities	36,019	54,716	34,738
Short-term borrowings	357,595	310,463	311,471
Federal Home Loan Bank (FHLB) advances	0	34,289	37,237
Total liabilities	5,584,919	5,320,911	4,982,318
Shareholders’ equity:	'	'	'
Preferred stock, no par value: Authorized - 200,000 shares, none issued	0	0	0
Issued and outstanding — 29,778,250 shares at September 30, 2013, 27,498,868 shares at December 31, 2012 and 27,498,094 shares at September 30, 2012	29,778	27,499	27,498
Additional paid-in capital	487,176	433,195	432,627
Retained earnings	191,538	166,766	160,884
Accumulated other comprehensive loss	-35,175	-31,119	-22,906
Total shareholders’ equity	673,317	596,341	598,103
Total Liabilities and Shareholders’ Equity	$6,258,236	$5,917,252	$5,580,421

Consolidated_Statements_of_Fin1

Consolidated Statements of Financial Position (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, except Share data, unless otherwise specified
Held-to-maturity, fair value	$275,866	$229,922	$223,185
Accumulated depreciation of premises and equipment	$98,150	$93,207	$91,203
Preferred stock, no par value	'	'	'
Preferred stock, shares authorized	200,000	200,000	200,000
Preferred stock, shares issued	0	0	0
Common stock, par value	$1	$1	$1
Common stock, shares authorized	45,000,000	45,000,000	45,000,000
Common stock, shares issued	29,778,250	27,498,868	27,498,094
Common stock, shares outstanding	29,778,250	27,498,868	27,498,094

Consolidated_Statements_of_Inc

Consolidated Statements of Income (Unaudited) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Interest Income	'	'	'	'
Interest and fees on loans	$49,017	$48,322	$144,951	$144,472
Interest on investment securities:	'	'	'	'
Taxable	2,714	2,458	7,737	7,610
Tax-exempt	1,587	1,457	4,738	4,407
Dividends on nonmarketable equity securities	150	128	701	638
Interest on deposits with the Federal Reserve Bank	110	136	611	505
Total interest income	53,578	52,501	158,738	157,632
Interest Expense	'	'	'	'
Interest on deposits	4,160	5,238	12,990	16,999
Interest on short-term borrowings	124	105	359	317
Interest on FHLB advances	0	248	47	765
Total interest expense	4,284	5,591	13,396	18,081
Net Interest Income	49,294	46,910	145,342	139,551
Provision for loan losses	3,000	4,500	9,000	13,500
Net interest income after provision for loan losses	46,294	42,410	136,342	126,051
Noninterest Income	'	'	'	'
Service charges and fees on deposit accounts	5,690	5,028	16,420	14,546
Wealth management revenue	3,369	2,745	10,693	8,835
Other charges and fees for customer services	4,272	3,435	13,226	10,484
Mortgage banking revenue	1,038	1,457	4,699	4,059
Gain on sale of investment securities	0	0	1,104	0
Gain on sale of merchant card services	0	0	0	1,280
Other	275	54	689	784
Total noninterest income	14,644	12,719	46,831	39,988
Operating Expenses	'	'	'	'
Salaries, wages and employee benefits	24,065	20,738	72,062	61,846
Occupancy	3,406	3,137	10,449	9,264
Equipment and software	3,354	3,406	10,251	9,651
Other	8,720	9,442	29,781	29,132
Total operating expenses	39,545	36,723	122,543	109,893
Income before income taxes	21,393	18,406	60,630	56,146
Federal income tax expense	6,400	5,300	18,200	16,800
Net Income	$14,993	$13,106	$42,430	$39,346
Net Income Per Common Share:	'	'	'	'
Basic (in dollars per share)	$0.54	$0.48	$1.54	$1.43
Diluted (in dollars per share)	$0.53	$0.48	$1.53	$1.43
Cash Dividends Declared Per Common Share (dollars per share)	$0.22	$0.21	$0.64	$0.61

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Unaudited) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net income	$14,993	$13,106	$42,430	$39,346
Other comprehensive income (loss), net of tax:	'	'	'	'
Net unrealized gains (losses) on investment securities available-for-sale, net of tax expense (benefit) of $(392) and $491 for the three months ended September 30, 2013 and 2012, respectively, and $(2,879) and $746 for the nine months ended September 30, 2013 and 2012, respectively	-726	911	-5,347	1,385
Reclassification adjustment for realized gain on sale of investment securities available-for-sale included in net income, net of tax expense of $300 for the nine months ended September 30, 2013	0	0	-558	0
Adjustment for pension and other postretirement benefits, net of tax expense of $332 and $187 for the three months ended September 30, 2013 and 2012, respectively, and $996 and $559 for the nine months ended September 30, 2013 and 2012, respectively	616	347	1,849	1,038
Total other comprehensive income (loss), net of tax	-110	1,258	-4,056	2,423
Comprehensive income	$14,883	$14,364	$38,374	$41,769

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Tax expense (benefit) on net unrealized gains (losses) on investment securities available-for-sale	($392)	$491	($2,879)	$746
Tax expense (benefit) on reclassification adjustment for realized gains on sale of investment securities available-for-sale	0	0	300	0
Tax expense on adjustment for pension and other postretirement benefits	$332	$187	$996	$559

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (USD $)	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
In Thousands, unless otherwise specified
Beginning Balance at Dec. 31, 2011	$571,729	$27,457	$431,277	$138,324	($25,329)
Changes in Stockholders' Equity [Roll Forward]	'	'	'	'	'
Comprehensive income (loss)	41,769	'	'	39,346	2,423
Cash dividends declared per share: $0.61 and $0.64 per share for the nine months ended September 30, 2012 and September 30, 2013, respectively	-16,786	'	'	-16,786	'
Stock issued - stock options	11	1	10	'	'
Shares issued – directors’ stock plans	323	16	307	'	'
Shares issued – restricted stock units	-248	24	-272	'	'
Share-based compensation	1,305	'	1,305	'	'
Ending Balance at Sep. 30, 2012	598,103	27,498	432,627	160,884	-22,906
Beginning Balance at Dec. 31, 2012	596,341	27,499	433,195	166,766	-31,119
Changes in Stockholders' Equity [Roll Forward]	'	'	'	'	'
Comprehensive income (loss)	38,374	'	'	42,430	-4,056
Cash dividends declared per share: $0.61 and $0.64 per share for the nine months ended September 30, 2012 and September 30, 2013, respectively	-17,658	'	'	-17,658	'
Issuance of common stock, net of issuance costs	53,925	2,214	51,711	'	'
Stock issued - stock options	278	29	249	'	'
Shares issued – directors’ stock plans	305	13	292	'	'
Shares issued – restricted stock units	-379	23	-402	'	'
Share-based compensation	2,131	'	2,131	'	'
Ending Balance at Sep. 30, 2013	$673,317	$29,778	$487,176	$191,538	($35,175)

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Cash dividends declared per share	$0.22	$0.21	$0.64	$0.61

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (Unaudited) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Operating Activities	'	'
Net income	$42,430	$39,346
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Provision for loan losses	9,000	13,500
Gains on sales of loans	-6,041	-6,439
Proceeds from sales of loans	181,644	235,010
Loans originated for sale	-165,845	-224,828
Net gains on sales of other real estate and repossessed assets	-2,265	-1,498
Depreciation of premises and equipment	6,552	6,052
Amortization of intangible assets	2,794	2,935
Gain on sale of investment securities	-1,104	0
Net amortization of premiums and discounts on investment securities	3,054	3,774
Share-based compensation expense	2,131	1,305
Contributions to defined benefit pension plan	-15,000	-12,000
Net decrease in interest receivable and other assets	6,634	12,690
Net decrease in interest payable and other liabilities	-786	-5,673
Net cash provided by operating activities	63,198	64,174
Investment securities – available-for-sale:	'	'
Proceeds from sales	38,028	0
Proceeds from maturities, calls and principal reductions	121,959	189,681
Purchases	-289,189	-170,667
Investment securities – held-to-maturity:	'	'
Proceeds from maturities, calls and principal reductions	51,962	43,578
Purchases	-104,733	-81,734
Net increase in loans	-371,423	-216,285
Proceeds from sales of other real estate and repossessed assets	13,229	18,787
Purchases of premises and equipment and branch bank property, net of disposals	-5,166	-7,851
Net cash used in investing activities	-545,333	-224,491
Financing Activities	'	'
Net increase in interest- and noninterest-bearing demand deposits and savings accounts	393,262	333,771
Net decrease in time deposits	-123,400	-101,756
Net increase in short-term borrowings	47,132	7,685
Repayment of FHLB advances	-34,289	-5,820
Cash dividends paid	-17,658	-16,786
Proceeds from issuance of common stock, net of issuance costs	53,925	0
Proceeds from directors’ stock plans and exercise of stock options, net of shares withheld	517	251
Shares issued, net of shares withheld, for restricted stock units	-379	-248
Net cash provided by financing activities	319,110	217,097
Net increase (decrease) in cash and cash equivalents	-163,025	56,780
Cash and cash equivalents at beginning of period	656,135	381,940
Cash and cash equivalents at end of period	493,110	438,720
Supplemental Disclosure of Cash Flow Information:	'	'
Interest paid	13,888	18,625
Loans transferred to other real estate and repossessed assets	4,528	11,272
Closed branch offices transferred to other real estate	382	0
Federal income taxes paid	$12,950	$5,339

Significant_Accounting_Policie

Significant Accounting Policies	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Significant Accounting Policies	'
	Significant Accounting Policies
	Nature of Operations
	Chemical Financial Corporation (Corporation) operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operates through one commercial bank, Chemical Bank. Chemical Bank operates within the State of Michigan as a state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of four regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the bank’s geographical market areas. The products and services offered by the regional banking units, through branch banking offices, are generally consistent throughout the Corporation, as is the pricing of those products and services. The marketing of products and services throughout the Corporation’s regional banking units is generally uniform, as many of the markets served by the regional banking units overlap. The distribution of products and services is uniform throughout the Corporation’s regional banking units and is achieved primarily through retail branch banking offices, automated teller machines and electronically accessed banking products.
	The Corporation’s primary sources of revenue are interest from its loan products and investment securities, service charges and fees from customer deposit accounts and wealth management revenue.
	Basis of Presentation
	The accompanying unaudited consolidated financial statements of the Corporation and its subsidiaries have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, the consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s consolidated financial statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2012. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments believed necessary to present fairly the financial condition and results of operations of the Corporation for the periods presented. Operating results for the nine months ended September 30, 2013 are not necessarily indicative of the results that may be expected for the year ending December 31, 2013.
	Use of Estimates
	Management makes estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying footnotes. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, expected cash flows from acquired loans, fair value amounts related to business combinations, pension expense, income taxes, goodwill impairment and those assets that require fair value measurement. Actual results could differ from these estimates.
	Reclassifications
	Certain amounts in the consolidated statements of income for the three and nine months ended September 30, 2012 have been reclassified to conform with the 2013 presentation. Such reclassifications had no effect on the Corporation's assets, liabilities, shareholders' equity or net income.
	Originated Loans
	Originated loans include all of the Corporation's portfolio loans, excluding loans acquired on April 30, 2010 in the acquisition of O.A.K. Financial Corporation (OAK). Originated loans also include loans acquired as part of the Corporation's branch acquisition on December 7, 2012, as these loans were performing and were considered high-quality loans in accordance with the Corporation's credit underwriting standards at that date. Originated loans are stated at their principal amount outstanding, net of unearned income, charge-offs and unamortized deferred fees and costs. Loan interest income is recognized on the accrual basis. Deferred loan fees and costs are amortized over the loan term based on the level-yield method. Net loan commitment fees are deferred and amortized into fee income on a straight-line basis over the commitment period.
	The past due status of a loan is based on the loan’s contractual terms. A loan is placed in nonaccrual status (accrual of interest is discontinued) when principal or interest is past due 90 days or more (except for a loan that is secured by residential real estate, which is transferred to nonaccrual status at 120 days past due), unless the loan is both well-secured and in the process of collection, or earlier when, in the opinion of management, there is sufficient reason to doubt the collectibility of principal or interest. Interest previously accrued, but not collected, is reversed and charged against interest income at the time the loan is placed in nonaccrual status. Subsequent receipts of interest while a loan is in nonaccrual status are recorded as a reduction of principal. Loans are returned to accrual status when principal and interest payments are brought current, payments have been received consistently for a period of time (generally six months) and collectibility is no longer in doubt.
	Loans Acquired in a Business Combination
	Loans acquired in a business combination (acquired loans) consist of loans acquired on April 30, 2010 in the acquisition of OAK. Acquired loans were recorded at fair value at the date of acquisition, without a carryover of the associated allowance for loan losses related to these loans, through a fair value discount that was, in part, attributable to deterioration in credit quality. The estimate of expected credit losses was determined based on due diligence performed by executive and senior officers of the Corporation, with assistance from third-party consultants. The fair value discount was recorded as a reduction of the acquired loans’ outstanding principal balances in the consolidated statement of financial position at the acquisition date.
	The Corporation accounts for acquired loans, which are recorded at fair value at acquisition, in accordance with Accounting Standards Codifications (ASC) Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality (ASC 310-30). ASC 310-30 allows investors to aggregate loans acquired into loan pools that have common risk characteristics and thereby use a composite interest rate and expectation of cash flows expected to be collected for the loan pools. Under the provisions of ASC 310-30, the Corporation aggregated acquired loans into 14 pools based upon common risk characteristics, including types of loans, commercial type loans with similar risk grades and whether loans were performing or nonperforming. A pool is considered a single unit of accounting for purposes of applying the guidance prescribed in ASC 310-30. A loan will be removed from a pool of acquired loans only if the loan is sold, foreclosed, paid off or written off, and will be removed from the pool at the carrying value. If an individual loan is removed from a pool of loans, the difference between its relative carrying amount and the cash, fair value of the collateral, or other assets received would not affect the effective yield used to recognize the accretable difference on the remaining pool. The Corporation estimated the cash flows expected to be collected over the life of the pools of loans at acquisition, and estimates expected cash flows quarterly thereafter, based on a set of assumptions including expectations as to default rates, prepayment rates and loss severities. The Corporation must make numerous assumptions, interpretations and judgments using internal and third-party credit quality information to determine whether it is probable that the Corporation will be able to collect all contractually required payments. This is a point in time assessment and inherently subjective due to the nature of the available information and judgment involved.
	The calculation of the fair value of the acquired loan pools entails estimating the amount and timing of cash flows attributable to both principal and interest expected to be collected on such loan pools and then discounting those cash flows at market interest rates. The excess of a loan pool's expected cash flows at the acquisition date over its estimated fair value is referred to as the "accretable yield," which is recognized into interest income over the estimated remaining life of the loan pool on a level-yield basis. The difference between a loan pool's contractually required principal and interest payments at the acquisition date and the cash flows expected to be collected at the acquisition date is referred to as the "nonaccretable difference," which includes an estimate of future credit losses expected to be incurred over the estimated life of the loan pool and interest payments that are not expected to be collected. Decreases to the expected cash flows in each loan pool in subsequent periods will require the Corporation to record a provision for loan losses. Improvements in expected cash flows in each loan pool in subsequent periods will result in reversing a portion of the nonaccretable difference, which is then classified as part of the accretable yield and subsequently recognized into interest income over the estimated remaining life of the loan pool.
	Loans Modified Under Troubled Debt Restructurings
	Loans modified under troubled debt restructurings (TDRs) involve granting a concession to a borrower who is experiencing financial difficulty. Concessions generally include modifications to original loan terms, including changes to a loan’s payment schedule or interest rate, which generally would not otherwise be considered. The Corporation’s loans reported as TDRs consist of originated loans that continue to accrue interest at the loan’s original interest rate as the Corporation expects to collect the remaining principal and interest on the loan. The Corporation’s loans reported as TDRs do not include loans that are in a nonaccrual status that have been modified by the Corporation due to the borrower experiencing financial difficulty and for which a concession has been granted, as the Corporation does not expect to collect the full amount of principal and interest owed from the borrower on these modified loans. The interest income recognized on TDRs may include accretion of an identified impairment at the time of modification which is attributable to a temporary reduction in the borrower’s interest rate. At the time of modification, a TDR is reported as a nonperforming loan (nonperforming TDR) until a six-month payment history of principal and interest payments, in accordance with the terms of the loan modification, is sustained, at which time the Corporation moves the loan to a performing status (performing TDR). All TDRs are accounted for as impaired loans and are included in the Corporation’s analysis of the allowance for loan losses. A TDR that has been renewed for a borrower who is no longer experiencing financial difficulty and which yields a market rate of interest at the time of a renewal is no longer reported as a TDR in the first quarter following the calendar year in which the renewal took place.
	Loans in the Corporation’s commercial loan portfolio (comprised of commercial, commercial real estate, real estate construction and land development loans) that meet the definition of a TDR generally consist of loans where the Corporation has allowed borrowers to defer scheduled principal payments and make interest-only payments for a specified period of time at the stated interest rate of the original loan agreement or reduced payments due to a moderate extension of the loan’s contractual term. The Corporation does not expect to incur a loss on these loans based on its assessment of the borrowers’ expected cash flows, as the pre- and post-modification effective yields are approximately the same for these loans. Accordingly, no additional provision for loan losses has been recognized related to these loans. Since no loss is expected to be incurred on these loans, the loans accrue interest at the loan’s contractual interest rate. These loans are individually evaluated for impairment and transferred to nonaccrual status if it is probable that any remaining principal and interest payments due on the loans will not be collected in accordance with the modified terms of the loans.
	Loans in the Corporation’s consumer loan portfolio (comprised of residential mortgage, consumer installment and home equity loans) that meet the definition of a TDR generally include a concession that reduces a borrower’s monthly payments by decreasing the interest rate charged on the loan for a specified period of time (generally 24 months) under a formal modification agreement. The Corporation recognizes an additional provision for loan losses related to impairment on these loans on an individual basis based on the present value of expected future cash flows discounted at the loan’s original effective interest rate. These loans continue to accrue interest at the loan's effective interest rate, which consists of contractual interest under the terms of the modification agreement in addition to an adjustment for the accretion of computed impairment. These loans are moved to nonaccrual status if they become 90 days past due as to principal or interest, or sooner if conditions warrant.
	Impaired Loans
	A loan is defined to be impaired when it is probable that payment of principal and interest will not be made in accordance with the original contractual terms of the loan agreement. Impaired loans include nonaccrual loans, TDRs (nonperforming and performing) and acquired loans that were not performing in accordance with original contractual terms. Impaired loans are accounted for at the lower of the present value of expected cash flows discounted at the loan's effective interest rate or the estimated fair value of the collateral, if the loan is collateral dependent. When the present value of expected cash flows or the fair value of collateral of an impaired loan in the originated loan portfolio is less than the amount of unpaid principal outstanding on the loan, the principal balance of the loan is reduced to its carrying value through either an allocation of the allowance for loan losses or a partial charge-off of the loan balance.
	Nonperforming Loans
	Nonperforming loans are comprised of loans for which the accrual of interest has been discontinued (nonaccrual loans), accruing originated loans contractually past due 90 days or more as to interest or principal payments and nonperforming TDRs.
	Allowance for Loan Losses
	The allowance for loan losses (allowance) is presented as a reserve against loans. The allowance represents management’s assessment of probable loan losses inherent in the Corporation’s loan portfolio.
	Management’s evaluation of the adequacy of the allowance is based on a continuing review of the loan portfolio, actual loan loss experience, the underlying value of the collateral, risk characteristics of the loan portfolio, the level and composition of nonperforming loans, the financial condition of the borrowers, the balance of the loan portfolio, loan growth, economic conditions, employment levels in the Corporation’s local markets, and special factors affecting specific business sectors. The Corporation maintains formal policies and procedures to monitor and control credit risk. Management evaluates the allowance on a quarterly basis in an effort to ensure the level is appropriate to absorb probable losses inherent in the loan portfolio.
	The allowance provides for probable losses that have been identified with specific customer relationships and for probable losses believed to be incurred in the remainder of the originated loan portfolio, but that have not been specifically identified. The Corporation utilizes its own loss experience to estimate inherent losses on loans. Internal risk ratings are assigned to each loan in the commercial loan portfolio (commercial, commercial real estate, real estate construction and land development loans) at the time of approval and are subject to subsequent periodic reviews by senior management. The Corporation performs a detailed credit quality review quarterly on all loans greater than $0.25 million that have deteriorated below certain levels of credit risk and may allocate a specific portion of the allowance to such loans based upon this review. A portion of the allowance is allocated to the remaining loans by applying projected loss ratios, based on numerous factors. Projected loss ratios incorporate factors such as recent charge-off experience, trends with respect to adversely risk-rated loans in the commercial loan portfolio, trends with respect to past due and nonaccrual loans, changes in economic conditions and trends, changes in the value of underlying collateral and other credit risk factors. This evaluation involves a high degree of uncertainty.
	In determining the allowance and the related provision for loan losses, the Corporation considers four principal elements: (i) valuation allowances based upon probable losses identified during the review of impaired loans in the commercial loan portfolio, (ii) allocations established for adversely-rated loans in the commercial loan portfolio and nonaccrual residential mortgage, consumer installment and home equity loans, (iii) allocations, by loan classes, on all other loans based principally on a five-year historical loan loss experience and loan loss trends and (iv) an unallocated allowance based on the imprecision in the overall allowance methodology for loans collectively evaluated for impairment.
	Although the Corporation allocates portions of the allowance to specific loans and loan types, the entire allowance attributable to originated loans is available for any loan losses that occur in the originated portfolio. Loans that are deemed not collectible are charged off and reduce the allowance. The provision for loan losses and recoveries on loans previously charged off increase the allowance. Collection efforts may continue and recoveries may occur after a loan is charged off.
	Acquired loans are aggregated into pools based upon common risk characteristics. An allowance may be recorded related to an acquired loan pool if it experiences a decrease in expected cash flows, as compared to those projected at the acquisition date. On a quarterly basis, the expected future cash flow of each pool is estimated based on various factors, including changes in property values of collateral dependent loans, default rates, loss severities and prepayment speeds. Decreases in estimates of expected cash flows within a pool generally result in a charge to the provision for loan losses and a corresponding increase in the allowance allocated to acquired loans for the particular pool. Increases in estimates of expected cash flows within a pool generally result in a reduction in the allowance allocated to acquired loans for the particular pool, if applicable, and then an adjustment to the accretable yield for the pool, which will increase amounts recognized in interest income in subsequent periods.
	Various regulatory agencies, as an integral part of their examination process, periodically review the allowance. Such agencies may require additions to the allowance, based on their judgment, reflecting information available to them at the time of their examinations.
	Fair Value Measurements
	Fair value for assets and liabilities measured at fair value on a recurring or nonrecurring basis refers to the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants in the market in which the reporting entity transacts such sales or transfers based on the assumptions market participants would use when pricing an asset or liability. Assumptions are developed based on prioritizing information within a fair value hierarchy that gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data, such as the reporting entity’s own data.
	The Corporation may choose to measure eligible items at fair value at specified election dates. Unrealized gains and losses on items for which the fair value measurement option has been elected are reported in earnings at each subsequent reporting date. The fair value option (i) may be applied instrument by instrument, with certain exceptions, allowing the Corporation to record identical financial assets and liabilities at fair value or by another measurement basis permitted under GAAP, (ii) is irrevocable (unless a new election date occurs) and (iii) is applied only to entire instruments and not to portions of instruments. At September 30, 2013, December 31, 2012 and September 30, 2012, the Corporation elected the fair value option on all of its loans held-for-sale. The Corporation has not elected the fair value option for any other financial assets or liabilities.
	Share-Based Compensation
	The Corporation grants stock options, stock awards, restricted stock performance units and restricted stock service-based units to certain executive and senior management employees. The Corporation accounts for share-based compensation expense using the modified-prospective transition method. Under that method, compensation expense is recognized for stock options based on the estimated grant date fair value as computed using the Black-Scholes option pricing model and the probability of issuance. The Corporation accounts for stock awards based on the closing stock price of the Corporation's common stock on the date of the award. The fair values of both stock options and stock awards are recognized as compensation expense on a straight-line basis over the requisite service period. The Corporation accounts for restricted stock performance units based on the closing stock price of the Corporation's common stock on the date of grant, discounted by the present value of estimated future dividends to be declared over the requisite performance or service period. The fair value of restricted stock performance units is recognized as compensation expense over the expected requisite performance period, or requisite service period for awards with multiple performance and service conditions. The Corporation accounts for restricted stock service-based units based on the closing stock price of the Corporation's common stock on the date of grant, as these awards accrue dividend equivalents equal to the amount of any cash dividends that would have been payable to a shareholder owning the number of shares of the Corporation's common stock represented by the restricted stock service-based units. The fair value of the restricted stock service-based units is recognized as compensation expense over the requisite service period.
	Cash flows realized from the tax benefits of exercised stock option awards that result from actual tax deductions that are in excess of the recorded tax benefits related to the compensation expense recognized for those options (excess tax benefits) are classified as financing activities on the consolidated statements of cash flows.
	Income and Other Taxes
	The Corporation is subject to the income and other tax laws of the United States, the State of Michigan and other states where nexus has been created. These laws are complex and are subject to different interpretations by the taxpayer and the various taxing authorities. In determining the provision for income and other taxes, management must make judgments and estimates about the application of these inherently complex laws, related regulations and case law. In the process of preparing the Corporation’s tax returns, management attempts to make reasonable interpretations of enacted tax laws. These interpretations are subject to challenge by the tax authorities upon audit or to reinterpretation based on management’s ongoing assessment of facts and evolving case law.
	On a quarterly basis, management assesses the reasonableness of its estimated annual effective federal tax rate based upon its current best estimate of taxable income and the applicable taxes expected for the full year. Deferred tax assets and liabilities are reassessed on a quarterly basis, including the need for a valuation allowance for deferred tax assets.
	Uncertain income tax positions are evaluated to determine whether it is more-likely-than-not that a tax position will be sustained upon examination based on the technical merits of the tax position. If a tax position is more-likely-than-not to be sustained, a tax benefit is recognized for the amount that is greater than 50% likely to be realized. Reserves for contingent income tax liabilities attributable to unrecognized tax benefits associated with uncertain tax positions are reviewed quarterly for adequacy based upon developments in tax law and the status of audits or examinations. The Corporation had no contingent income tax liabilities recorded at September 30, 2013, December 31, 2012 or September 30, 2012. The tax periods open to examination by the Internal Revenue Service include the calendar years ended December 31, 2012, 2011 and 2010.
	Shareholders’ Equity
	Common Stock Repurchase Programs
	From time to time, the board of directors of the Corporation approves common stock repurchase programs allowing management to repurchase shares of the Corporation’s common stock in the open market. The repurchased shares are available for later reissuance in connection with potential future stock dividends, the Corporation’s dividend reinvestment plan, employee benefit plans and other general corporate purposes. Under these programs, the timing and actual number of shares subject to repurchase are at the discretion of management and are contingent on a number of factors, including the projected parent company cash flow requirements and the Corporation’s market price per share.
	In January 2008, the board of directors of the Corporation authorized the repurchase of up to 500,000 shares of the Corporation’s common stock under a stock repurchase program. In November 2011, the board of directors of the Corporation reaffirmed the stock buy-back authorization with the qualification that the shares may only be repurchased if the share price is below the tangible book value per share of the Corporation’s common stock at the time of the repurchase. Since the January 2008 authorization, no shares have been repurchased. At September 30, 2013, there were 500,000 remaining shares available for repurchase under the Corporation’s stock repurchase programs.
	Preferred Stock
	On April 20, 2009, the shareholders of the Corporation authorized the board of directors of the Corporation to issue up to 200,000 shares of preferred stock in connection with either an acquisition by the Corporation of an entity that has shares of preferred stock issued and outstanding pursuant to any program established by the United States government or participation by the Corporation in any program established by the United States government. At September 30, 2013, no shares of preferred stock were issued and outstanding.
	Legal Matters
	The Corporation and Chemical Bank are subject to certain legal actions arising in the ordinary course of business. In the opinion of management, after consultation with legal counsel, the ultimate disposition of these matters is not expected to have a material adverse effect on the consolidated financial condition or results of operations of the Corporation.
	Adopted Accounting Pronouncements
	In February 2013, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2013-02, Comprehensive Income (Topic 220): Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income (ASU 2013-02). Under ASU 2013-02, an entity is required to provide information about the amounts reclassified out of Accumulated Other Comprehensive Income (AOCI) by component. In addition, an entity is required to present, either on the face of the financial statements or in the notes, significant amounts reclassified out of AOCI by the respective line items of net income, but only if the amount reclassified is required to be reclassified in its entirety in the same reporting period. For amounts that are not required to be reclassified in their entirety to net income, an entity is required to cross-reference to other disclosures that provide additional details about those amounts. ASU 2013-02 does not change the requirements for reporting net income or other comprehensive income in the financial statements. ASU 2013-02 is effective for interim and annual periods beginning on or after December 15, 2012. The adoption of ASU 2013-02 as of January 1, 2013 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
	Pending Accounting Pronouncements
	In February 2013, the FASB issued ASU 2013-04, Liabilities (Topic 405): Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation is Fixed at the Reporting Date (ASU 2013-04). ASU 2013-04 provides guidance in relation to the recognition, measurement and disclosure of obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date. ASU 2013-04 is effective for interim and annual periods beginning after December 15, 2013 and should be applied retrospectively for all periods presented for those obligations resulting from joint and several liability arrangements that exist at the beginning of the fiscal year of adoption. The adoption of ASU 2013-04 is not expected to have a material impact on the Corporation's consolidated financial condition or results of operations.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
Acquisitions	'
	Acquisitions
	Acquisition of 21 Branches
	On December 7, 2012, Chemical Bank acquired 21 branches from Independent Bank, a subsidiary of Independent Bank Corporation. In addition to the branch offices, which are located in the Northeast and Battle Creek regions of Michigan, the acquisition included $404 million in deposits and $44 million in loans. The purchase price of the branch offices, including equipment, was $8.1 million and the Corporation paid a premium on deposits of $11.5 million, or approximately 2.85% of total deposits. The loans were purchased at a discount of 1.75%.
	In connection with the acquisition of the branches, the Corporation recorded $6.8 million of goodwill and $5.6 million of other intangible assets attributable to customer core deposits.
	Acquisition of O.A.K. Financial Corporation (OAK)
	On April 30, 2010, the Corporation acquired OAK for total consideration of $83.7 million. OAK, a bank holding company, owned Byron Bank, which provided traditional banking services and products through 14 banking offices serving communities in Ottawa, Allegan and Kent counties in west Michigan. Byron Bank was consolidated with and into Chemical Bank on July 23, 2010. At the acquisition date, OAK had total assets of $820 million, including total loans of $627 million, and total deposits of $693 million, including brokered deposits of $193 million.
	Upon acquisition, the OAK loan portfolio had contractually required principal and interest payments receivable of $683 million and $97 million, respectively, expected principal and interest cash flows of $636 million and $88 million, respectively, and a fair value of $627 million. The difference between the contractually required payments receivable and the expected cash flows represents the nonaccretable difference, which totaled $56 million at the acquisition date, with $47 million attributable to expected credit losses. The difference between the expected cash flows and fair value represents the accretable yield, which totaled $97 million at the acquisition date. The outstanding contractual principal balance and the carrying amount of the acquired loan portfolio were $334 million and $309 million, respectively, at September 30, 2013, compared to $419 million and $393 million, respectively, at December 31, 2012 and $440 million and $413 million, respectively, at September 30, 2012.
	Activity for the accretable yield, which includes contractually due interest for acquired loans that have been renewed or extended since the date of acquisition and continue to be accounted for in loan pools in accordance with ASC 310-30, follows:
			Nine Months Ended
			September 30,
			2013			2012
			(In thousands)
	Balance at beginning of period		$	49,390		$	68,305
	Additions (reductions)*		(997		)	6,237
	Accretion recognized in interest income		(13,235		)	(18,543		)
	Reclassification from nonaccretable difference		125			—
	Balance at end of period		$	35,283		$	55,999
	*	Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.

Investment_Securities

Investment Securities	9 Months Ended
	Sep. 30, 2013
Investments, Debt and Equity Securities [Abstract]	'
Investment Securities	'
	Investment Securities
	The following is a summary of the amortized cost and fair value of investment securities available-for-sale and investment securities held-to-maturity at September 30, 2013, December 31, 2012 and September 30, 2012:
		Investment Securities Available-for-Sale
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	30-Sep-13
	Government sponsored agencies	$	86,065	$	264	$	404	$	85,925
	State and political subdivisions	44,191		1,386		5		45,572
	Residential mortgage-backed securities	310,550		1,144		3,534		308,160
	Collateralized mortgage obligations	200,407		199		2,148		198,458
	Corporate bonds	65,053		583		202		65,434
	Preferred stock	1,389		208		—		1,597
	Total	$	707,655	$	3,784	$	6,293	$	705,146
	31-Dec-12
	Government sponsored agencies	$	97,529	$	241	$	213	$	97,557
	State and political subdivisions	47,663		2,302		—		49,965
	Residential mortgage-backed securities	96,320		3,100		9		99,411
	Collateralized mortgage obligations	262,790		984		182		263,592
	Corporate bonds	69,788		546		539		69,795
	Preferred stock	6,144		345		—		6,489
	Total	$	580,234	$	7,518	$	943	$	586,809
	30-Sep-12
	Government sponsored agencies	$	101,576	$	182	$	266	$	101,492
	State and political subdivisions	49,707		2,538		7		52,238
	Residential mortgage-backed securities	101,709		3,543		16		105,236
	Collateralized mortgage obligations	297,960		1,392		274		299,078
	Corporate bonds	82,219		509		622		82,106
	Preferred stock	6,144		284		—		6,428
	Total	$	639,315	$	8,448	$	1,185	$	646,578
		Investment Securities Held-to-Maturity
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	30-Sep-13
	State and political subdivisions	$	272,079	$	5,978	$	8,441	$	269,616
	Trust preferred securities	10,500		—		4,250		6,250
	Total	$	282,579	$	5,978	$	12,691	$	275,866
	31-Dec-12
	State and political subdivisions	$	219,477	$	8,087	$	3,367	$	224,197
	Trust preferred securities	10,500		—		4,775		5,725
	Total	$	229,977	$	8,087	$	8,142	$	229,922
	30-Sep-12
	State and political subdivisions	$	211,036	$	8,661	$	1,712	$	217,985
	Trust preferred securities	10,500		—		5,300		5,200
	Total	$	221,536	$	8,661	$	7,012	$	223,185
	The majority of the Corporation’s residential mortgage-backed securities and collateralized mortgage obligations are backed by a U.S. government agency (Government National Mortgage Association) or a government sponsored enterprise (Federal Home Loan Mortgage Corporation or Federal National Mortgage Association).
	During the second quarter of 2013, the Corporation sold a $4.8 million preferred stock investment security, which was carried at cost, and recognized a gross gain on the sale of $0.2 million.
	At September 30, 2013, the Corporation held $10.5 million of trust preferred investment securities that were recorded as held-to-maturity, with $10.0 million of these securities representing a 100% interest in a trust preferred investment security of a small non-public bank holding company in Michigan that has been assessed by the Corporation as financially strong. The remaining $0.5 million represents a 10% interest in another trust preferred investment security of a small non-public bank holding company located in Michigan that was categorized as well-capitalized under regulatory guidelines at September 30, 2013.
	At September 30, 2013, it was the Corporation’s opinion that the market for trust preferred investment securities was not active, and thus, in accordance with GAAP, when there is a significant decrease in the volume and activity for an asset or liability in relation to normal market activity, adjustments to transaction or quoted prices may be necessary or a change in valuation technique or multiple valuation techniques may be appropriate. The Corporation obtained pricing information for its trust preferred investment securities from an independent third-party pricing source. The pricing information was based on both observable inputs and appropriate risk adjustments that market participants would make for possible nonperformance, illiquidity and issuer specifics such as size, leverage position and location. The observable inputs were based on the existing market and insight into appropriate rate of return adjustments that market participants would require for the additional risk associated with a single issue investment security of this nature. Based on the information obtained from the independent third-party pricing source, the Corporation calculated a fair value at September 30, 2013 of $6.0 million on its $10.0 million trust preferred investment security and $0.2 million on its $0.5 million trust preferred investment security, resulting in a combined unrealized loss of $4.3 million at that date. At September 30, 2013, the Corporation concluded that the $4.3 million of combined unrealized loss on the trust preferred investment securities was temporary in nature.
	The following is a summary of the amortized cost and fair value of investment securities at September 30, 2013, by maturity, for both available-for-sale and held-to-maturity investment securities. The maturities of residential mortgage-backed securities and collateralized mortgage obligations are based on scheduled principal payments. The maturities of all other debt securities are based on final contractual maturity.
		30-Sep-13
		Amortized		Fair Value
		Cost
		(In thousands)
	Investment Securities Available-for-Sale:
	Due in one year or less	$	91,500	$	91,946
	Due after one year through five years	117,337		118,555
	Due after five years through ten years	426,031		422,118
	Due after ten years	71,398		70,930
	Preferred stock	1,389		1,597
	Total	$	707,655	$	705,146
	Investment Securities Held-to-Maturity:
Due in one year or less	$	42,112	$	42,179
Due after one year through five years	114,020		115,646
Due after five years through ten years	74,316		74,353
Due after ten years	52,131		43,688
Total	$	282,579	$	275,866
The following schedule summarizes information for both available-for-sale and held-to-maturity investment securities with gross unrealized losses at September 30, 2013, December 31, 2012 and September 30, 2012, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position.
	Less Than 12 Months				12 Months or More				Total
	Fair		Gross		Fair		Gross		Fair		Gross
	Value		Unrealized		Value		Unrealized		Value		Unrealized
			Losses				Losses				Losses
	(In thousands)
30-Sep-13
Government sponsored agencies	$	43,816	$	223	$	14,395	$	181	$	58,211	$	404
State and political subdivisions	120,232		6,918		30,915		1,528		151,147		8,446
Residential mortgage-backed securities	267,495		3,532		40		2		267,535		3,534
Collateralized mortgage obligations	129,049		1,617		15,302		531		144,351		2,148
Corporate bonds	9,926		85		19,883		117		29,809		202
Trust preferred securities	—		—		6,250		4,250		6,250		4,250
Total	$	570,518	$	12,375	$	86,785	$	6,609	$	657,303	$	18,984
31-Dec-12
Government sponsored agencies	$	46,103	$	213	$	—	$	—	$	46,103	$	213
State and political subdivisions	70,675		2,257		8,046		1,110		78,721		3,367
Residential mortgage-backed securities	273		1		1,305		8		1,578		9
Collateralized mortgage obligations	19,331		10		36,835		172		56,166		182
Corporate bonds	4,747		253		34,707		286		39,454		539
Trust preferred securities	—		—		5,725		4,775		5,725		4,775
Total	$	141,129	$	2,734	$	86,618	$	6,351	$	227,747	$	9,085
30-Sep-12
Government sponsored agencies	$	39,729	$	248	$	8,808	$	18	$	48,537	$	266
State and political subdivisions	69,841		1,711		1,533		8		71,374		1,719
Residential mortgage-backed securities	32		1		19,704		15		19,736		16
Collateralized mortgage obligations	12,036		45		47,066		229		59,102		274
Corporate bonds	19,469		531		24,900		91		44,369		622
Trust preferred securities	—		—		5,200		5,300		5,200		5,300
Total	$	141,107	$	2,536	$	107,211	$	5,661	$	248,318	$	8,197
An assessment is performed quarterly by the Corporation to determine whether unrealized losses in its investment securities portfolio are temporary or other-than-temporary by carefully considering all available information. The Corporation reviews factors such as financial statements, credit ratings, news releases and other pertinent information of the underlying issuer or company to make its determination. Management did not believe any individual unrealized loss on any investment security, as of September 30, 2013, represented an other-than-temporary impairment (OTTI). Management believed that the unrealized losses on investment securities at September 30, 2013 were temporary in nature and due primarily to changes in interest rates, increased credit spreads and reduced market liquidity and not as a result of credit-related issues. Unrealized losses of $4.3 million in the trust preferred securities portfolio, related to trust preferred securities of two well-capitalized bank holding companies in Michigan, were attributable to the illiquidity in financial markets for these types of investments. The Corporation performed an analysis of the creditworthiness of these issuers and concluded that, at September 30, 2013, the Corporation expected to recover the entire amortized cost basis of these investment securities.
At September 30, 2013, the Corporation did not have the intent to sell any of its impaired investment securities and believed that it was more-likely-than-not that the Corporation will not have to sell any such investment securities before a full recovery of amortized cost. Accordingly, at September 30, 2013, the Corporation believed the impairments in its investment securities portfolio were temporary in nature. However, there is no assurance that OTTI may not occur in the future.

Loans

Loans	9 Months Ended
	Sep. 30, 2013
Receivables [Abstract]	'
Loans	'
	Loans
	Loan portfolio segments are defined as the level at which an entity develops and documents a systematic methodology to determine its allowance. The Corporation has two loan portfolio segments (commercial loans and consumer loans) that it uses in determining the allowance. Both quantitative and qualitative factors are used by management at the loan portfolio segment level in determining the adequacy of the allowance for the Corporation. Classes of loans are a disaggregation of an entity’s loan portfolio segments. Classes of loans are defined as a group of loans which share similar initial measurement attributes, risk characteristics, and methods for monitoring and assessing credit risk. The Corporation has seven classes of loans, which are set forth below.
	Commercial — Loans and lines of credit to varying types of businesses, including municipalities, school districts and nonprofit organizations, for the purpose of supporting working capital, operational needs and term financing of equipment. Repayment of such loans is generally provided through operating cash flows of the business. Commercial loans are predominately secured by equipment, inventory, accounts receivable, personal guarantees of the owner and other sources of repayment, although the Corporation may also secure commercial loans with real estate.
	Commercial real estate — Loans secured by real estate occupied by the borrower for ongoing operations, non-owner occupied real estate leased to one or more tenants and vacant land that has been acquired for investment or future land development.
	Real estate construction — Secured loans for the construction of business properties. Real estate construction loans often convert to a commercial real estate loan at the completion of the construction period.
	Land development — Secured development loans made to borrowers for the purpose of infrastructure improvements to vacant land to create finished marketable residential and commercial lots/land. Most land development loans are originated with the intention that the loans will be paid through the sale of developed lots/land by the developers within twelve months of the completion date. Land development loans at September 30, 2013, December 31, 2012 and September 30, 2012 were primarily comprised of loans to develop residential properties.
	Residential mortgage — Loans secured by one- to four-family residential properties, generally with fixed interest rates for periods of fifteen years or less. The loan-to-value ratio at the time of origination is generally 80% or less. Residential mortgage loans with a loan-to-value ratio of more than 80% generally require private mortgage insurance.
	Consumer installment — Loans to consumers primarily for the purpose of acquiring automobiles, recreational vehicles and personal watercraft. These loans consist of relatively small amounts that are spread across many individual borrowers.
	Home equity — Loans and lines of credit whereby consumers utilize equity in their personal residence, generally through a second mortgage, as collateral to secure the loan.
	Commercial, commercial real estate, real estate construction and land development loans are referred to as the Corporation’s commercial loan portfolio, while residential mortgage, consumer installment and home equity loans are referred to as the Corporation’s consumer loan portfolio. A summary of loans follows:
		September 30,				December 31,				September 30,
		2013				2012				2012
		(In thousands)
	Commercial loan portfolio:
	Commercial	$	1,128,122			$	1,002,722			$	951,938
	Commercial real estate	1,215,631				1,161,861				1,117,073
	Real estate construction	78,361				62,689				56,071
	Land development	23,673				37,548				34,811
	Subtotal	2,445,787				2,264,820				2,159,893
	Consumer loan portfolio:
	Residential mortgage	942,777				883,835				880,295
	Consumer installment	622,040				546,036				538,412
	Home equity	512,067				473,044				440,559
	Subtotal	2,076,884				1,902,915				1,859,266
	Total loans	$	4,522,671			$	4,167,735			$	4,019,159
	Credit Quality Monitoring
	The Corporation maintains loan policies and credit underwriting standards as part of the process of managing credit risk. These standards include making loans generally only within the Corporation’s market areas. The Corporation’s lending markets generally consist of communities across the lower peninsula of Michigan, except for the southeastern portion of Michigan. The Corporation has no foreign loans.
	The Corporation has a commercial loan portfolio approval process involving underwriting and individual and group loan approval authorities to consider credit quality and loss exposure at loan origination. The loans in the Corporation’s commercial loan portfolio are risk rated at origination based on the grading system set forth below. The approval authority of relationship managers is established based on experience levels, with credit decisions greater than $1.0 million requiring group loan authority approval, except for four executive and senior officers who have varying limits exceeding $1.5 million and up to $3.5 million. With respect to the group loan authorities, the Corporation has a loan committee, consisting of certain executive and senior officers, that meets weekly to consider loans ranging in amounts from $1.0 million to $5.0 million, depending on risk rating and credit action required. A directors’ loan committee, consisting of nine members of the board of directors, including the chief executive officer and senior credit officer, meets bi-weekly to consider loans in amounts over $5.0 million, and certain loans under $5.0 million depending on a loan’s risk rating and credit action required. Loans over $10.0 million require majority approval of the full board of directors.
	The majority of the Corporation’s consumer loan portfolio is comprised of secured loans that are relatively small. The Corporation’s consumer loan portfolio has a centralized approval process that utilizes standardized underwriting criteria. The ongoing measurement of credit quality of the consumer loan portfolio is largely done on an exception basis. If payments are made on schedule, as agreed, then no further monitoring is performed. However, if delinquency occurs, the delinquent loans are turned over to the Corporation’s collection department for resolution, resulting in repossession or foreclosure if payments are not brought current. Credit quality for the entire consumer loan portfolio is measured by the periodic delinquency rate, nonaccrual amounts and actual losses incurred.
	Loans in the commercial loan portfolio tend to be larger and more complex than those in the consumer loan portfolio, and therefore, are subject to more intensive monitoring. All loans in the commercial loan portfolio have an assigned relationship manager, and most borrowers provide periodic financial and operating information that allows the relationship managers to stay abreast of credit quality during the life of the loans. The risk ratings of loans in the commercial loan portfolio are reassessed at least annually, with loans below an acceptable risk rating reassessed more frequently and reviewed by various loan committees within the Corporation at least quarterly.
	The Corporation maintains a centralized independent loan review function that monitors the approval process and ongoing asset quality of the loan portfolio, including the accuracy of loan grades. The Corporation periodically utilizes independent third-party service providers to assist with its loan review function. The Corporation also maintains an independent appraisal review function that participates in the review of all appraisals obtained by the Corporation for loans in the commercial loan portfolio.
	Credit Quality Indicators
	Commercial Loan Portfolio
	The Corporation uses a nine grade risk rating system to monitor the ongoing credit quality of its commercial loan portfolio. These loan grades rank the credit quality of a borrower by measuring liquidity, debt capacity, coverage and payment behavior as shown in the borrower’s financial statements. The loan grades also measure the quality of the borrower’s management and the repayment support offered by any guarantors. A summary of the Corporation’s loan grades (or characteristics of the loans within each grade) follows:
	Risk Grades 1-5 (Acceptable Credit Quality) — All loans in risk grades 1 through 5 are considered to be acceptable credit risks by the Corporation and are grouped for purposes of allowance for loan loss considerations and financial reporting. The five grades essentially represent a ranking of loans that are all viewed to be of acceptable credit quality, taking into consideration the various factors mentioned above, but with varying degrees of financial strength, debt coverage, management and factors that could impact credit quality. Business credits within risk grades 1 through 5 range from Risk Grade 1: Prime Quality (factors include: excellent business credit; excellent debt capacity and coverage; outstanding management; strong guarantors; superior liquidity and net worth; favorable loan-to-value ratios; debt secured by cash or equivalents, or backed by the full faith and credit of the U.S. Government) to Risk Grade 5: Acceptable Quality With Care (factors include: acceptable business credit, but with added risk due to specific industry or internal situations).
	Risk Grade 6 (Watch) — A business credit that is not acceptable within the Corporation’s loan origination criteria; cash flow may not be adequate or is continually inconsistent to service current debt; financial condition has deteriorated as company trends/management have become inconsistent; the company is slow in furnishing quality financial information; working capital needs of the company are reliant on short-term borrowings; personal guarantees are weak and/or with little or no liquidity; the net worth of the company has deteriorated after recent or continued losses; the loan requires constant monitoring and attention from the Corporation; payment delinquencies becoming more serious; if left uncorrected, these potential weaknesses may, at some future date, result in deterioration of repayment prospects.
	Risk Grade 7 (Substandard — Accrual) — A business credit that is inadequately protected by the current financial net worth and paying capacity of the obligor or of the collateral pledged, if any; management has deteriorated or has become non-existent; quality financial information is not available; a high level of maintenance is required by the Corporation; cash flow can no longer support debt requirements; loan payments are continually and/or severely delinquent; negative net worth; personal guaranty has become insignificant; a credit that has a well-defined weakness or weaknesses that jeopardize the liquidation of the debt. The Corporation still expects a full recovery of all contractual principal and interest payments; however, a possibility exists that the Corporation will sustain some loss if deficiencies are not corrected.
	Risk Grade 8 (Substandard — Nonaccrual) — A business credit accounted for on a nonaccrual basis that has all the weaknesses inherent in a loan classified as risk grade 7 with the added characteristic that the weaknesses are so pronounced that, on the basis of current financial information, conditions, and values, collection in full is highly questionable; a partial loss is possible and interest is no longer being accrued. This loan meets the definition of an impaired loan. The risk of loss requires analysis to determine whether a valuation allowance needs to be established.
	Risk Grade 9 (Substandard — Doubtful) — A business credit that has all the weaknesses inherent in a loan classified as risk grade 8 and interest is no longer being accrued, but additional deficiencies make it highly probable that liquidation will not satisfy the majority of the obligation; the primary source of repayment is nonexistent and there is doubt as to the value of the secondary source of repayment; the possibility of loss is likely, but current pending factors could strengthen the credit. This loan meets the definition of an impaired loan. A loan charge-off is recorded when management deems an amount uncollectible; however, the Corporation will establish a valuation allowance for probable losses, if required.
	The Corporation considers all loans graded 1 through 5 as acceptable credit risks and structures and manages such relationships accordingly. Periodic financial and operating data combined with regular loan officer interactions are deemed adequate to monitor borrower performance. Loans graded 6 and 7 are considered higher-risk credits than loans graded 1 through 5 and the frequency of loan officer contact and receipt of financial data is increased to stay abreast of borrower performance. Loans graded 8 and 9 are considered problematic and require special care. Further, loans graded 6 through 9 are managed and monitored regularly through a number of processes, procedures and committees, including oversight by a loan administration committee comprised of executive and senior management of the Corporation, which include highly structured reporting of financial and operating data, intensive loan officer intervention and strategies to exit, as well as potential management by the Corporation’s special assets group.
	The following schedule presents the recorded investment of loans in the commercial loan portfolio by risk rating categories at September 30, 2013, December 31, 2012 and September 30, 2012:
		Commercial				Real Estate				Real Estate				Land				Total
						Commercial				Construction				Development
		(In thousands)
	30-Sep-13
	Originated Portfolio:
	Risk Grades 1-5	$	974,903			$	963,394			$	64,210			$	7,760			$	2,010,267
	Risk Grade 6	16,439				37,572				58				1,063				55,132
	Risk Grade 7	37,644				30,969				1,337				4,870				74,820
	Risk Grade 8	9,753				28,186				183				2,954				41,076
	Risk Grade 9	2,056				437				—				—				2,493
	Subtotal	1,040,795				1,060,558				65,788				16,647				2,183,788
	Acquired Portfolio:
	Risk Grades 1-5	82,648				141,234				12,573				4,604				241,059
	Risk Grade 6	2,620				4,837				—				—				7,457
	Risk Grade 7	992				7,847				—				—				8,839
	Risk Grade 8	1,067				1,155				—				2,422				4,644
	Risk Grade 9	—				—				—				—				—
	Subtotal	87,327				155,073				12,573				7,026				261,999
	Total	$	1,128,122			$	1,215,631			$	78,361			$	23,673			$	2,445,787
	31-Dec-12
	Originated Portfolio:
	Risk Grades 1-5	$	827,112			$	846,901			$	47,847			$	15,010			$	1,736,870
Risk Grade 6	38,066				45,261				59				497				83,883
Risk Grade 7	16,831				26,343				—				6,367				49,541
Risk Grade 8	12,540				33,345				1,217				4,184				51,286
Risk Grade 9	2,061				4,315				—				—				6,376
Subtotal	896,610				956,165				49,123				26,058				1,927,956
Acquired Portfolio:
Risk Grades 1-5	93,281				188,499				13,566				8,419				303,765
Risk Grade 6	8,225				5,900				—				237				14,362
Risk Grade 7	2,169				9,677				—				—				11,846
Risk Grade 8	2,437				1,620				—				2,834				6,891
Risk Grade 9	—				—				—				—				—
Subtotal	106,112				205,696				13,566				11,490				336,864
Total	$	1,002,722			$	1,161,861			$	62,689			$	37,548			$	2,264,820
30-Sep-12
Originated Portfolio:
Risk Grades 1-5	$	772,555			$	793,237			$	37,346			$	12,348			$	1,615,486
Risk Grade 6	33,819				38,880				18				1,092				73,809
Risk Grade 7	17,091				30,971				—				5,313				53,375
Risk Grade 8	14,790				38,369				933				5,731				59,823
Risk Grade 9	427				2,942				—				—				3,369
Subtotal	838,682				904,399				38,297				24,484				1,805,862
Acquired Portfolio:
Risk Grades 1-5	97,308				192,903				17,774				7,556				315,541
Risk Grade 6	10,899				7,006				—				—				17,905
Risk Grade 7	2,107				11,672				—				—				13,779
Risk Grade 8	2,942				1,093				—				2,771				6,806
Risk Grade 9	—				—				—				—				—
Subtotal	113,256				212,674				17,774				10,327				354,031
Total	$	951,938			$	1,117,073			$	56,071			$	34,811			$	2,159,893
Consumer Loan Portfolio
The Corporation evaluates the credit quality of loans in the consumer loan portfolio based on the performing or nonperforming status of the loan. Loans in the consumer loan portfolio that are performing in accordance with original contractual terms and are less than 90 days past due and accruing interest are considered to be in a performing status, while those that are in nonaccrual status, contractually past due 90 days or more as to interest or principal payments or classified as a nonperforming TDR are considered to be in a nonperforming status. Loans in the consumer loan portfolio that are reported as TDRs are considered in a nonperforming status until they meet the Corporation’s definition of a performing TDR, at which time they are considered in a performing status.
The following schedule presents the recorded investment of loans in the consumer loan portfolio based on loans in a performing status and loans in a nonperforming status at September 30, 2013, December 31, 2012 and September 30, 2012:
	Residential Mortgage				Consumer				Home Equity				Total
					Installment								Consumer
	(In thousands)
30-Sep-13
Originated Loans:
Performing	$	918,931			$	619,346			$	475,439			$	2,013,716
Nonperforming	11,850				665				3,709				16,224
Subtotal	930,781				620,011				479,148				2,029,940
Acquired Loans:
Performing	11,918				2,029				32,737				46,684
Nonperforming	78				—				182				260
Subtotal	11,996				2,029				32,919				46,944
Total	$	942,777			$	622,040			$	512,067			$	2,076,884
31-Dec-12
Originated Loans:
Performing	$	854,882			$	543,339			$	429,734			$	1,827,955
Nonperforming	14,988				739				3,502				19,229
Subtotal	869,870				544,078				433,236				1,847,184
Acquired Loans:
Performing	13,843				1,958				39,637				55,438
Nonperforming	122				—				171				293
Subtotal	13,965				1,958				39,808				55,731
Total	$	883,835			$	546,036			$	473,044			$	1,902,915
30-Sep-12
Originated Loans:
Performing	$	849,385			$	535,277			$	395,411			$	1,780,073
Nonperforming	15,640				962				4,010				20,612
Subtotal	865,025				536,239				399,421				1,800,685
Acquired Loans:
Performing	14,928				2,173				40,874				57,975
Nonperforming	342				—				264				606
Subtotal	15,270				2,173				41,138				58,581
Total	$	880,295			$	538,412			$	440,559			$	1,859,266
Nonperforming Loans
A summary of nonperforming loans follows:
	September 30,				December 31,				September 30,
	2013				2012				2012
	(In thousands)
Nonaccrual loans:
Commercial	$	11,809			$	14,601			$	15,217
Commercial real estate	28,623				37,660				41,311
Real estate construction	183				1,217				933
Land development	2,954				4,184				5,731
Residential mortgage	8,029				10,164				11,307
Consumer installment	665				739				876
Home equity	3,023				2,733				2,949
Total nonaccrual loans	55,286				71,298				78,324
Accruing loans contractually past due 90 days or more as to interest or principal payments:
Commercial	281				—				273
Commercial real estate	—				87				247
Real estate construction	—				—				—
Land development	—				—				—
Residential mortgage	692				1,503				431
Consumer installment	—				—				—
Home equity	686				769				1,147
Total accruing loans contractually past due 90 days or more as to interest or principal payments	1,659				2,359				2,098
Nonperforming TDRs:
Commercial loan portfolio	15,744				13,876				6,553
Consumer loan portfolio	3,129				3,321				3,902
Total nonperforming TDRs	18,873				17,197				10,455
Total nonperforming loans	$	75,818			$	90,854			$	90,877
The Corporation’s loans reported as TDRs do not include loans that are in a nonaccrual status that have been modified by the Corporation due to the borrower experiencing financial difficulty and for which a concession has been granted, as the Corporation does not expect to collect the full amount of principal and interest owed from the borrower on these modified loans. The Corporation’s nonaccrual loans at September 30, 2013, December 31, 2012 and September 30, 2012 included $39.1 million, $47.5 million and $37.0 million, respectively, of these modified loans.
Impaired Loans
The following schedule presents impaired loans by classes of loans at September 30, 2013, December 31, 2012 and September 30, 2012:
	Recorded				Unpaid				Related
	Investment				Principal				Valuation
					Balance				Allowance
	(In thousands)
30-Sep-13
Impaired loans with a valuation allowance:
Commercial	$	5,059			$	5,803			$	1,857
Commercial real estate	6,684				7,901				1,651
Real estate construction	183				253				33
Land development	517				653				97
Residential mortgage	17,731				17,731				585
Subtotal	30,174				32,341				4,223
Impaired loans with no related valuation allowance:
Commercial	21,543				25,642				—
Commercial real estate	43,178				57,256				—
Real estate construction	133				133				—
Land development	9,095				13,347				—
Residential mortgage	8,029				8,029				—
Consumer installment	665				665				—
Home equity	3,023				3,023				—
Subtotal	85,666				108,095				—
Total impaired loans:
Commercial	26,602				31,445				1,857
Commercial real estate	49,862				65,157				1,651
Real estate construction	316				386				33
Land development	9,612				14,000				97
Residential mortgage	25,760				25,760				585
Consumer installment	665				665				—
Home equity	3,023				3,023				—
Total	$	115,840			$	140,436			$	4,223
31-Dec-12
Impaired loans with a valuation allowance:
Commercial	$	6,368			$	6,818			$	1,966
Commercial real estate	17,267				17,607				5,359
Real estate construction	171				171				75
Land development	254				254				50
Residential mortgage	18,901				18,901				658
Subtotal	42,961				43,751				8,108
Impaired loans with no related valuation allowance:
Commercial	23,230				27,959				—
Commercial real estate	37,223				48,531				—
Real estate construction	1,046				1,116				—
Land development	10,867				15,112				—
Residential mortgage	10,164				10,164				—
Consumer installment	739				739				—
Home equity	2,733				2,733				—
Subtotal	86,002				106,354				—
Total impaired loans:
Commercial	29,598				34,777				1,966
Commercial real estate	54,490				66,138				5,359
Real estate construction	1,217				1,287				75
Land development	11,121				15,366				50
Residential mortgage	29,065				29,065				658
Consumer installment	739				739				—
Home equity	2,733				2,733				—
Total	$	128,963			$	150,105			$	8,108
	Recorded				Unpaid				Related
	Investment				Principal				Valuation
					Balance				Allowance
	(In thousands)
30-Sep-12
Impaired loans with a valuation allowance:
Commercial	$	6,743			$	7,357			$	2,240
Commercial real estate	19,694				22,593				5,344
Real estate construction	127				127				43
Land development	2,800				2,800				383
Residential mortgage	15,958				15,958				649
Subtotal	45,322				48,835				8,659
Impaired loans with no related valuation allowance:
Commercial	19,768				24,517				—
Commercial real estate	36,225				48,187				—
Real estate construction	806				806				—
Land development	7,723				10,903				—
Residential mortgage	14,907				14,907				—
Consumer installment	876				876				—
Home equity	2,949				2,949				—
Subtotal	83,254				103,145				—
Total impaired loans:
Commercial	26,511				31,874				2,240
Commercial real estate	55,919				70,780				5,344
Real estate construction	933				933				43
Land development	10,523				13,703				383
Residential mortgage	30,865				30,865				649
Consumer installment	876				876				—
Home equity	2,949				2,949				—
Total	$	128,576			$	151,980			$	8,659
The difference between an impaired loan’s recorded investment and the unpaid principal balance for originated loans represents a partial charge-off resulting from a confirmed loss due to the value of the collateral securing the loan being below the loan balance and management’s assessment that full collection of the loan balance is not likely and for acquired loans that meet the definition of an impaired loan represents fair value adjustments recognized at the acquisition date attributable to expected credit losses and the discounting of expected cash flows at market interest rates. The difference between the recorded investment and the unpaid principal balance of $24.6 million, $21.1 million and $23.4 million at September 30, 2013, December 31, 2012 and September 30, 2012, respectively, includes confirmed losses (partial charge-offs) of $21.2 million, $17.3 million and $19.8 million, respectively, and fair value discount adjustments of $3.4 million, $3.8 million and $3.6 million, respectively.
Impaired loans included $7.6 million, $9.1 million and $9.4 million at September 30, 2013, December 31, 2012 and September 30, 2012, respectively, of acquired loans that were not performing in accordance with original contractual terms. Acquired loans that are not performing in accordance with contractual terms are not reported as nonperforming loans because these loans are recorded in pools at their net realizable value based on the principal and interest the Corporation expects to collect on these loans. Impaired loans also included $34.1 million, $31.4 million and $30.4 million at September 30, 2013, December 31, 2012 and September 30, 2012, respectively, of performing TDRs.
The following schedule presents information related to impaired loans for the three and nine months ended September 30, 2013 and 2012:
	Three Months Ended September 30, 2013								Nine Months Ended September 30, 2013
	Average				Interest  Income				Average				Interest  Income
	Recorded				Recognized				Recorded				Recognized
	Investment				While on				Investment				While on
					Impaired Status								Impaired Status
	(In thousands)
Commercial	$	27,025			$	215			$	26,894			$	633
Commercial real estate	50,266				284				53,482				984
Real estate construction	414				2				395				7
Land development	9,615				79				10,470				261
Residential mortgage	25,826				278				27,216				847
Consumer installment	632				—				666				—
Home equity	3,091				—				2,977				—
Total	$	116,869			$	858			$	122,100			$	2,732
	Three Months Ended September 30, 2012								Nine Months Ended September 30, 2012
	Average				Interest  Income				Average				Interest  Income
	Recorded				Recognized				Recorded				Recognized
	Investment				While on				Investment				While on
					Impaired Status								Impaired Status
	(In thousands)
Commercial	$	28,683			$	149			$	27,684			$	602
Commercial real estate	54,524				212				59,063				642
Real estate construction	912				—				470				—
Land development	10,582				71				8,869				216
Residential mortgage	33,652				288				37,861				1,031
Consumer installment	909				—				1,222				—
Home equity	2,940				—				2,910				—
Total	$	132,202			$	720			$	138,079			$	2,491
The following schedule presents the aging status of the recorded investment in loans by classes of loans at September 30, 2013, December 31, 2012 and September 30, 2012:
	31-60				61-89				Accruing				Non-accrual				Total				Current		Total
	Days				Days				Loans				Loans				Past Due						Loans
	Past Due				Past Due				Past Due
									90 Days
									or More
	(In thousands)
30-Sep-13
Originated Portfolio:
Commercial	$	7,833			$	1,542			$	281			$	11,809			$	21,465			$	1,019,330	$	1,040,795
Commercial real estate	6,533				2,274				—				28,623				37,430				1,023,128		1,060,558
Real estate construction	90				5,385				—				183				5,658				60,130		65,788
Land development	187				—				—				2,954				3,141				13,506		16,647
Residential mortgage	1,739				76				692				8,029				10,536				920,245		930,781
Consumer installment	2,980				350				—				665				3,995				616,016		620,011
Home equity	2,344				434				686				3,023				6,487				472,661		479,148
Total	$	21,706			$	10,061			$	1,659			$	55,286			$	88,712			$	4,125,016	$	4,213,728
Acquired Portfolio:
Commercial	$	67			$	—			$	1,574			$	—			$	1,641			$	85,686	$	87,327
Commercial real estate	439				—				3,355				—				3,794				151,279		155,073
Real estate construction	—				—				—				—				—				12,573		12,573
Land development	—				—				2,422				—				2,422				4,604		7,026
Residential mortgage	264				—				77				—				341				11,655		11,996
Consumer installment	3				1				—				—				4				2,025		2,029
Home equity	389				79				182				—				650				32,269		32,919
Total	$	1,162			$	80			$	7,610			$	—			$	8,852			$	300,091	$	308,943
	31-60				61-89				Accruing				Non-accrual				Total				Current		Total
	Days				Days				Loans				Loans				Past Due						Loans
	Past Due				Past Due				Past Due
									90 Days
									or More
	(In thousands)
31-Dec-12
Originated Portfolio:
Commercial	$	3,999			$	730			$	—			$	14,601			$	19,330			$	877,280	$	896,610
Commercial real estate	5,852				2,089				87				37,660				45,688				910,477		956,165
Real estate construction	—				—				—				1,217				1,217				47,906		49,123
Land development	—				—				—				4,184				4,184				21,874		26,058
Residential mortgage	3,161				55				1,503				10,164				14,883				854,987		869,870
Consumer installment	2,415				378				—				739				3,532				540,546		544,078
Home equity	1,618				427				769				2,733				5,547				427,689		433,236
Total	$	17,045			$	3,679			$	2,359			$	71,298			$	94,381			$	3,680,759	$	3,775,140
Acquired Portfolio:
Commercial	$	—			$	—			$	2,834			$	—			$	2,834			$	103,278	$	106,112
Commercial real estate	287				15				3,139				—				3,441				202,255		205,696
Real estate construction	—				—				—				—				—				13,566		13,566
Land development	—				—				2,834				—				2,834				8,656		11,490
Residential mortgage	123				—				122				—				245				13,720		13,965
Consumer installment	10				—				—				—				10				1,948		1,958
Home equity	205				—				170				—				375				39,433		39,808
Total	$	625			$	15			$	9,099			$	—			$	9,739			$	382,856	$	392,595
30-Sep-12
Originated Portfolio:
Commercial	$	9,707			$	1,374			$	273			$	15,217			$	26,571			$	812,111	$	838,682
Commercial real estate	4,929				1,660				247				41,311				48,147				856,252		904,399
Real estate construction	—				—				—				933				933				37,364		38,297
Land development	48				—				—				5,731				5,779				18,705		24,484
Residential mortgage	3,208				97				431				11,307				15,043				849,982		865,025
Consumer installment	3,299				470				—				876				4,645				531,594		536,239
Home equity	1,543				730				1,147				2,949				6,369				393,052		399,421
Total	$	22,734			$	4,331			$	2,098			$	78,324			$	107,487			$	3,499,060	$	3,606,547
Acquired Portfolio:
Commercial	$	—			$	15			$	3,356			$	—			$	3,371			$	109,885	$	113,256
Commercial real estate	1,262				—				2,390				—				3,652				209,022		212,674
Real estate construction	—				—				—				—				—				17,774		17,774
Land development	—				—				3,038				—				3,038				7,289		10,327
Residential mortgage	80				—				343				—				423				14,847		15,270
Consumer installment	18				—				—				—				18				2,155		2,173
Home equity	138				39				264				—				441				40,697		41,138
Total	$	1,498			$	54			$	9,391			$	—			$	10,943			$	401,669	$	412,612
Loans Modified Under Troubled Debt Restructurings (TDRs)
The following schedule presents the Corporation’s loans reported as TDRs at September 30, 2013, December 31, 2012 and September 30, 2012:
	Performing				Nonperforming				Total
	(In thousands)
30-Sep-13
Commercial loan portfolio	$	19,469			$	15,744			$	35,213
Consumer loan portfolio	14,602				3,129				17,731
Total	$	34,071			$	18,873			$	52,944
31-Dec-12
Commercial loan portfolio	$	15,789			$	13,876			$	29,665
Consumer loan portfolio	15,580				3,321				18,901
Total	$	31,369			$	17,197			$	48,566
30-Sep-12
Commercial loan portfolio	$	14,750			$	6,553			$	21,303
Consumer loan portfolio	15,656				3,902				19,558
Total	$	30,406			$	10,455			$	40,861
The following schedule provides information on loans reported as performing and nonperforming TDRs that were either modified during the three and nine months ended September 30, 2013 and 2012 or modified during a previous period and transfered from nonaccrual status during the three and nine months ended September 30, 2013 and 2012:
	Three Months Ended September 30, 2013											Nine Months Ended September 30, 2013
	Number			Pre-				Post-				Number			Pre-				Post-
	of  Loans			Modification				Modification				of  Loans			Modification				Modification
				Recorded				Recorded							Recorded				Recorded
				Investment				Investment							Investment				Investment
	(Dollars in thousands)
Commercial loan portfolio:
Commercial	2			$	352			$	352			11			$	3,370			$	3,370
Commercial real estate	3			2,100				2,100				16			8,701				8,701
Land development	—			—				—				3			637				637
Subtotal – commercial loan portfolio	5			2,452				2,452				30			12,708				12,708
Consumer loan portfolio (residential mortgage)	19			1,647				1,604				48			3,534				3,435
Total	24			$	4,099			$	4,056			78			$	16,242			$	16,143
	Three Months Ended September 30, 2012											Nine Months Ended September 30, 2012
	Number			Pre-				Post-				Number			Pre-				Post-
	of  Loans			Modification				Modification				of  Loans			Modification				Modification
				Recorded				Recorded							Recorded				Recorded
				Investment				Investment							Investment				Investment
	(Dollars in thousands)
Commercial loan portfolio:
Commercial	9			$	665			$	665			19			$	3,891			$	3,891
Commercial real estate	8			1,426				1,426				19			5,264				5,264
Land development	—			—				—				1			1,638				1,638
Subtotal – commercial loan portfolio	17			2,091				2,091				39			10,793				10,793
Consumer loan portfolio (residential mortgage)	15			1,352				1,301				65			7,083				6,872
Total	32			$	3,443			$	3,392			104			$	17,876			$	17,665
The pre-modification and post-modification recorded investment represents amounts as of the date of loan modification. The difference between the pre-modification and post-modification recorded investment of residential mortgage TDRs represents impairment recognized by the Corporation through the provision for loan losses computed based on a loan's post-modification present value of expected future cash flows discounted at the loan's original effective interest rate. No provision for loan losses was recognized related to TDRs in the commercial loan portfolio as the Corporation does not expect to incur a loss on these loans based on its assessment of the borrower's expected cash flows.
The following schedule includes loans reported as performing and nonperforming TDRs at September 30, 2013 and 2012, and TDRs that were transferred to nonaccrual status during the three and nine months ended September 30, 2013 and 2012, for which there was a payment default during the three and nine months ended September 30, 2013 and 2012, whereby the borrower was past due with respect to principal and/or interest for 90 days or more, and the loan became a TDR during the twelve-month period prior to the default:
	Three Months Ended September 30, 2013							Nine Months Ended September 30, 2013
	Number of			Principal Balance at End of Period				Number of			Principal Balance at End of Period
	Loans							Loans
	(Dollars in thousands)
Commercial loan portfolio:
Commercial	1			$	748			2			$	1,182
Commercial real estate	4			2,833				4			2,833
Subtotal – commercial loan portfolio	5			3,581				6			4,015
Consumer loan portfolio (residential mortgage)	4			109				7			478
Total	9			$	3,690			13			$	4,493
	Three Months Ended September 30, 2012							Nine Months Ended September 30, 2012
	Number of			Principal Balance at End of Period				Number of			Principal Balance at End of Period
	Loans							Loans
	(Dollars in thousands)
Commercial loan portfolio:
Commercial	2			$	1,240			3			$	1,300
Commercial real estate	3			2,457				5			3,293
Subtotal – commercial loan portfolio	5			3,697				8			4,593
Consumer loan portfolio (residential mortgage)	1			742				5			1,126
Total	6			$	4,439			13			$	5,719
Allowance for Loan Losses
The following schedule presents, by loan portfolio segment, the changes in the allowance for the three and nine months ended September 30, 2013 and details regarding the balance in the allowance and the recorded investment in loans at September 30, 2013 by impairment evaluation method.
	Commercial				Consumer				Unallocated				Total
	Loan				Loan
	Portfolio				Portfolio
	(In thousands)
Changes in allowance for loan losses for the three months ended September 30, 2013:
Beginning balance	$	47,780			$	28,745			$	5,659			$	82,184
Provision for loan losses	2,810				2,165				(1,975		)		3,000
Charge-offs	(2,637		)		(1,793		)		—				(4,430		)
Recoveries	374				404				—				778
Ending balance	$	48,327			$	29,521			$	3,684			$	81,532
Changes in allowance for loan losses for the nine months ended September 30, 2013:
Beginning balance	$	49,975			$	29,333			$	5,183			$	84,491
Provision for loan losses	5,815				4,684				(1,499		)		9,000
Charge-offs	(9,374		)		(5,891		)		—				(15,265		)
Recoveries	1,911				1,395				—				3,306
Ending balance	$	48,327			$	29,521			$	3,684			$	81,532
Allowance for loan losses balance at September 30, 2013 attributable to:
Loans individually evaluated for impairment	$	3,638			$	585			$	—			$	4,223
Loans collectively evaluated for impairment	44,689				28,436				3,684				76,809
Loans acquired with deteriorated credit quality	—				500				—				500
Total	$	48,327			$	29,521			$	3,684			$	81,532
Recorded investment (loan balance) at September 30, 2013:
Loans individually evaluated for impairment	$	78,782			$	17,731			$	—			$	96,513
Loans collectively evaluated for impairment	2,105,006				2,012,209				—				4,117,215
Loans acquired with deteriorated credit quality	261,999				46,944				—				308,943
Total	$	2,445,787			$	2,076,884			$	—			$	4,522,671
The following schedule presents, by loan portfolio segment, details regarding the balance in the allowance and the recorded investment in loans at December 31, 2012 by impairment evaluation method.
	Commercial				Consumer				Unallocated				Total
	Loan				Loan
	Portfolio				Portfolio
	(In thousands)
Allowance for loan losses balance at December 31, 2012 attributable to:
Loans individually evaluated for impairment	$	7,450			$	658			$	—			$	8,108
Loans collectively evaluated for impairment	42,525				28,175				5,183				75,883
Loans acquired with deteriorated credit quality	—				500				—				500
Total	$	49,975			$	29,333			$	5,183			$	84,491
Recorded investment (loan balance) at December 31, 2012:
Loans individually evaluated for impairment	$	87,327			$	18,901			$	—			$	106,228
Loans collectively evaluated for impairment	1,840,629				1,828,283				—				3,668,912
Loans acquired with deteriorated credit quality	336,864				55,731				—				392,595
Total	$	2,264,820			$	1,902,915			$	—			$	4,167,735
The following schedule presents, by loan portfolio segment, the changes in the allowance for the three and nine months ended September 30, 2012 and details regarding the balance in the allowance and the recorded investment in loans at September 30, 2012 by impairment evaluation method.
	Commercial				Consumer				Unallocated				Total
	Loan				Loan
	Portfolio				Portfolio
	(In thousands)
Changes in allowance for loan losses for the three months ended September 30, 2012:
Beginning balance	$	53,759			$	29,784			$	3,168			$	86,711
Provision for loan losses	2,365				1,765				370				4,500
Charge-offs	(4,754		)		(2,842		)		—				(7,596		)
Recoveries	460				619				—				1,079
Ending balance	$	51,830			$	29,326			$	3,538			$	84,694
Changes in allowance for loan losses for the nine months ended September 30, 2012:
Beginning balance	$	55,645			$	29,166			$	3,522			$	88,333
Provision for loan losses	6,003				7,481				16				13,500
Charge-offs	(11,330		)		(8,985		)		—				(20,315		)
Recoveries	1,512				1,664				—				3,176
Ending balance	$	51,830			$	29,326			$	3,538			$	84,694
Allowance for loan losses balance at September 30, 2012 attributable to:
Loans individually evaluated for impairment	$	8,010			$	649			$	—			$	8,659
Loans collectively evaluated for impairment	43,820				28,177				3,538				75,535
Loans acquired with deteriorated credit quality	—				500				—				500
Total	$	51,830			$	29,326			$	3,538			$	84,694
Recorded investment (loan balance) at September 30, 2012:
Loans individually evaluated for impairment	$	84,495			$	19,558			$	—			$	104,053
Loans collectively evaluated for impairment	1,721,367				1,781,127				—				3,502,494
Loans acquired with deteriorated credit quality	354,031				58,581				—				412,612
Total	$	2,159,893			$	1,859,266			$	—			$	4,019,159
The allowance attributable to acquired loans of $0.5 million at September 30, 2013, December 31, 2012 and September 30, 2012 was primarily attributable to two consumer loan pools in the acquired loan portfolio experiencing a decline in expected cash flows. There were no material changes in expected cash flows for the remaining acquired loan pools at September 30, 2013, December 31, 2012 or September 30, 2012.

Intangible_Assets

Intangible Assets	9 Months Ended
	Sep. 30, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Intangible Assets	'
	Intangible Assets
	The Corporation has the following types of intangible assets: goodwill, core deposit intangible assets and mortgage servicing rights (MSRs). Goodwill and core deposit intangible assets arose as the result of business combinations or other acquisitions. MSRs arose as a result of selling residential mortgage loans in the secondary market while retaining the right to service these loans and receive servicing income over the life of the loan. Amortization is recorded on the core deposit intangible assets and MSRs. Goodwill is not amortized but is evaluated at least annually for impairment. The Corporation’s most recent annual goodwill impairment test was performed as of October 31, 2012, and no impairment existed for the Corporation’s goodwill at that date. No triggering events have occurred since the most recent annual goodwill impairment review that would require an interim valuation.
	The following table shows the net carrying value of the Corporation’s intangible assets:
		September 30,			December 31,			September 30,
		2013			2012			2012
		(In thousands)
	Goodwill	$	120,164		$	120,164		$	113,414
	Other intangible assets:
	Core deposit intangible assets	$	10,466		$	11,910		$	6,777
	Mortgage servicing rights	3,399			3,478			3,466
	Total other intangible assets	$	13,865		$	15,388		$	10,243
	The following table sets forth the carrying amount, accumulated amortization and amortization expense of core deposit intangible assets that are amortizable and arose from business combinations or other acquisitions:
		September 30,			December 31,			September 30,
		2013			2012			2012
		(In thousands)
	Gross original amount	$	18,659		$	18,659		$	26,468
	Accumulated amortization	8,193			6,749			19,691
	Carrying amount	$	10,466		$	11,910		$	6,777
	Amortization expense for the three months ended September 30	$	467					$	367
	Amortization expense for the nine months ended September 30	$	1,444					$	1,102
	At September 30, 2013, the remaining amortization expense on core deposit intangible assets that existed as of that date was estimated as follows: 2013 — $0.5 million; 2014 — $1.8 million; 2015 — $1.7 million; 2016 — $1.5 million; 2017 — $1.2 million; 2018 and thereafter — $3.8 million.
	The following shows the net carrying value and fair value of MSRs and the total loans that the Corporation is servicing for others:
		September 30,			December 31,			September 30,
		2013			2012			2012
		(In thousands)
	Net carrying value of MSRs	$	3,399		$	3,478		$	3,466
	Fair value of MSRs	$	6,839		$	4,716		$	4,277
	Loans serviced for others that have servicing rights capitalized	$	886,980		$	906,314		$	901,052
	The following table shows the activity for capitalized MSRs:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
		(In thousands)
	Balance at beginning of period	$	3,421		$	3,463		$	3,478		$	3,593
	Additions	311			503			1,271			1,706
	Amortization	(333		)	(500		)	(1,350		)	(1,833		)
	Balance at end of period	$	3,399		$	3,466		$	3,399		$	3,466
	There was no impairment valuation allowance recorded on MSRs as of September 30, 2013, December 31, 2012 or September 30, 2012.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Loss	9 Months Ended
	Sep. 30, 2013
Equity [Abstract]	'
Accumulated Other Comprehensive Loss	'
	Accumulated Other Comprehensive Loss
	The components of accumulated other comprehensive loss, net of related tax benefit/expense, were as follows:
		September 30,			December 31,			September 30,
		2013			2012			2012
		(In thousands)
	Net unrealized gains (losses) on investment securities – available-for-sale, net of related tax expense (benefit) of $(878) at September 30, 2013, $2,301 at December 31, 2012 and $2,542 at September 30, 2012	$	(1,631	)	$	4,274		$	4,721
	Pension and other postretirement benefits adjustment, net of related tax benefit of $18,062 at September 30, 2013, $19,058 at December 31, 2012 and $14,876 at September 30, 2012	(33,544		)	(35,393		)	(27,627		)
	Accumulated other comprehensive loss	$	(35,175	)	$	(31,119	)	$	(22,906	)

Regulatory_Capital

Regulatory Capital	9 Months Ended
	Sep. 30, 2013
Banking and Thrift [Abstract]	'
Regulatory Capital	'
	Regulatory Capital
	The Corporation and Chemical Bank are subject to various regulatory capital requirements administered by federal banking agencies. Under these capital requirements, Chemical Bank must meet specific capital guidelines that involve quantitative measures of assets and certain off-balance sheet items as calculated under regulatory accounting practices. In addition, capital amounts and classifications are subject to qualitative judgments by regulators. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Corporation’s consolidated financial statements.
	Federal and state banking regulations place certain restrictions on the transfer of assets, in the form of dividends, loans, or advances, from Chemical Bank to the Corporation. As of September 30, 2013, substantially all of the assets of Chemical Bank were restricted from transfer to the Corporation in the form of loans or advances. Dividends from Chemical Bank are the principal source of funds for the Corporation. As a member of the Federal Reserve System, Chemical Bank is subject to Regulation H, which among other things, provides that a member bank may not declare or pay a dividend during the calendar year which would exceed the bank's net income during the current calendar year and its retained net income for the prior two calendar years without regulatory approval. There are additional restrictions and prohibitions if a bank were to be less than well-capitalized.
	Quantitative measures established by regulation to ensure capital adequacy require minimum ratios of Tier 1 capital to average assets (Leverage Ratio) and Tier 1 and Total capital to risk-weighted assets. These capital guidelines assign risk weights to on- and off-balance sheet items in arriving at total risk-weighted assets. Minimum capital levels are based upon the perceived risk of various asset categories and certain off-balance sheet instruments. Risk weighted assets totaled $4.51 billion, $4.18 billion and $4.03 billion at September 30, 2013, December 31, 2012 and September 30, 2012, respectively.
	On September 18, 2013, the Corporation issued and sold 2,213,750 shares of common stock, including 288,750 shares of common stock that were issued and sold upon the exercise in full of the underwriters' over-allotment option, at a public offering price of $26.00 per share. The net proceeds from the issuance and sale of the common stock, after deducting the underwriting discount and issuance related expenses, totaled $53.9 million. The Corporation intends to use the net proceeds for general corporate purposes, which may include funding loan growth and long-term strategic opportunities that may arise in the future.
	At September 30, 2013, December 31, 2012 and September 30, 2012, Chemical Bank’s capital ratios exceeded the quantitative capital ratios required for an institution to be considered “well-capitalized.” Significant factors that may affect capital adequacy include, but are not limited to, a disproportionate growth in assets versus capital and a change in mix or credit quality of assets.
	The summary below compares the Corporation’s and Chemical Bank’s actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy:
		Actual				Minimum Required for Capital Adequacy Purposes				Required to be Well Capitalized Under Prompt Corrective Action Regulations
		Capital		Ratio		Capital		Ratio		Capital		Ratio
		Amount				Amount				Amount
		(Dollars in thousands)
	30-Sep-13
	Total Capital to Risk-Weighted Assets:
	Corporation	$	638,786	14.2	%	$	361,199	8	%	N/A		N/A
	Chemical Bank	568,626		12.6		360,617		8		$	450,771	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	582,039		12.9		180,600		4		N/A		N/A
	Chemical Bank	511,969		11.4		180,309		4		270,463		6
	Leverage Ratio:
	Corporation	582,039		10		232,972		4		N/A		N/A
	Chemical Bank	511,969		8.8		232,828		4		291,034		5
	31-Dec-12
	Total Capital to Risk-Weighted Assets:
	Corporation	$	552,171	13.2	%	$	334,140	8	%	N/A		N/A
	Chemical Bank	536,223		12.9		333,195		8		$	416,494	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	499,563		12		167,070		4		N/A		N/A
	Chemical Bank	483,761		11.6		166,598		4		249,896		6
	Leverage Ratio:
	Corporation	499,563		9.2		217,145		4		N/A		N/A
	Chemical Bank	483,761		8.9		216,784		4		270,980		5
	30-Sep-12
	Total Capital to Risk-Weighted Assets:
	Corporation	$	549,388	13.6	%	$	322,212	8	%	N/A		N/A
	Chemical Bank	537,467		13.4		321,585		8		$	401,982	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	498,618		12.4		161,106		4		N/A		N/A
	Chemical Bank	486,794		12.1		160,793		4		241,189		6
	Leverage Ratio:
	Corporation	498,618		9.4		211,670		4		N/A		N/A
	Chemical Bank	486,794		9.2		211,452		4		264,315		5

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements
	Fair value, as defined by GAAP, is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. A fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability or, in the absence of a principal market, the most advantageous market for the asset or liability. The price in the principal (or most advantageous) market used to measure the fair value of the asset or liability is not adjusted for transaction costs. An orderly transaction is a transaction that assumes exposure to the market for a period prior to the measurement date to allow for market activities that are usual and customary for transactions involving such assets and liabilities; it is not a forced transaction. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact and (iv) willing to transact.
	The Corporation utilizes fair value measurements to record fair value adjustments to certain assets and to determine fair value disclosures. Investment securities — available-for-sale and loans held-for-sale (for residential mortgage loan originations held-for-sale on or after July 1, 2012) are recorded at fair value on a recurring basis. Additionally, the Corporation may be required to record other assets, such as impaired loans, goodwill, other intangible assets, other real estate and repossessed assets, at fair value on a nonrecurring basis. These nonrecurring fair value adjustments typically involve the application of lower of cost or market accounting or write-downs of individual assets.
	The Corporation determines the fair value of its financial instruments based on a three-level hierarchy established by GAAP. The classification and disclosure of assets and liabilities within the hierarchy is based on whether the inputs to the valuation methodology used for measurement are observable or unobservable. Observable inputs reflect market-derived or market-based information obtained from independent sources, while unobservable inputs reflect management’s estimates about market data. The three levels of inputs that may be used to measure fair value within the GAAP hierarchy are as follows:
	Level 1	Valuation is based upon quoted prices for identical instruments traded in active markets. Level 1 valuations for the Corporation would include U.S. Treasury securities that are traded by dealers or brokers in active over-the-counter markets. Valuations are obtained from a third party pricing service for these investment securities.
	Level 2	Valuation is based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-based valuation techniques for which all significant assumptions are observable in the market. Level 2 valuations for the Corporation include government sponsored agency securities, including securities issued by the Federal Home Loan Bank, Federal Home Loan Mortgage Corporation, Federal National Mortgage Association, Federal Farm Credit Bank, Student Loan Marketing Corporation and the Small Business Administration, securities issued by certain state and political subdivisions, residential mortgage-backed securities, collateralized mortgage obligations, corporate bonds and preferred stock. Valuations are obtained from a third-party pricing service for these investment securities.
	Level 3	Valuation is generated from model-based techniques that use at least one significant assumption not observable in the market. These unobservable assumptions reflect estimates of assumptions that market participants would use in pricing the asset or liability. Valuation techniques include use of option pricing models, discounted cash flow models, yield curves and similar techniques. The determination of fair value requires management judgment or estimation and generally is corroborated by external data, which includes third-party pricing services. Level 3 valuations for the Corporation include securities issued by certain state and political subdivisions, trust preferred investment securities, impaired loans, goodwill, core deposit intangible assets, MSRs and other real estate and repossessed assets.
	A description of the valuation methodologies used for instruments measured at fair value, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below. These valuation methodologies were applied to all of the Corporation’s financial assets and financial liabilities carried at fair value and all financial instruments disclosed at fair value. In general, fair value is based upon quoted market prices, where available. If quoted market prices are not available, fair value is based upon third-party pricing services when available. Fair value may also be based on internally developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be required to record financial instruments at fair value. Any such valuation adjustments are applied consistently over time. The Corporation’s valuation methodologies may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values.
	While management believes the Corporation’s valuation methodologies are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. Furthermore, the fair value amounts may change significantly after the date of the statement of financial position from the amounts reported in the consolidated financial statements and related notes.
	Assets and Liabilities Recorded at Fair Value on a Recurring Basis
	Investment securities — available-for-sale are recorded at fair value on a recurring basis. Fair value measurement is based upon quoted prices, if available. If quoted prices are not available, fair values are generally measured using independent pricing models or other model-based valuation techniques that include market inputs, such as benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data and industry and economic events.
	The carrying amounts reported in the consolidated statements of financial position at September 30, 2013, December 31, 2012 and September 30, 2012 for loans held-for-sale is at fair value, as the Corporation elected the fair value option for all residential mortgage loans held-for-sale originated on or after July 1, 2012. The fair values of loans held-for-sale are based on the market price for similar loans sold in the secondary market, and therefore, are classified as Level 2 valuations.
	Disclosure of Recurring Basis Fair Value Measurements
	For assets measured at fair value on a recurring basis, quantitative disclosures about the fair value measurements for each major category of assets were as follows:
			Fair Value Measurements – Recurring Basis
			Quoted Prices				Significant				Significant				Total
			In Active				Other				Unobservable
			Markets for				Observable				Inputs
			Identical				Inputs				(Level 3)
			Assets				(Level 2)
			(Level 1)
			(In thousands)
	30-Sep-13
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—			$	85,925			$	—			$	85,925
	State and political subdivisions		—				45,572				—				45,572
	Residential mortgage-backed securities		—				308,160				—				308,160
	Collateralized mortgage obligations		—				198,458				—				198,458
	Corporate bonds		—				65,434				—				65,434
	Preferred stock		—				1,597				—				1,597
	Total investment securities – available-for-sale		—				705,146				—				705,146
	Loans held-for-sale		—				7,907				—				7,907
	Total assets measured at fair value on a recurring basis		$	—			$	713,053			$	—			$	713,053
	31-Dec-12
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—			$	97,557			$	—			$	97,557
	State and political subdivisions		—				49,965				—				49,965
	Residential mortgage-backed securities		—				99,411				—				99,411
	Collateralized mortgage obligations		—				263,592				—				263,592
	Corporate bonds		—				69,795				—				69,795
	Preferred stock		—				1,734				—				1,734
	Total investment securities – available-for-sale		—				582,054				—				582,054
	Loans held-for-sale		—				17,665				—				17,665
	Total assets measured at fair value on a recurring basis		$	—			$	599,719			$	—			$	599,719
	30-Sep-12
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—			$	101,492			$	—			$	101,492
	State and political subdivisions		—				52,238				—				52,238
	Residential mortgage-backed securities		—				105,236				—				105,236
	Collateralized mortgage obligations		—				299,078				—				299,078
	Corporate bonds		—				82,106				—				82,106
	Preferred stock		—				1,673				—				1,673
	Total investment securities – available-for-sale		—				641,823				—				641,823
	Loans held-for-sale		—				15,075				—				15,075
	Total assets measured at fair value on a recurring basis		$	—			$	656,898			$	—			$	656,898
	There were no liabilities recorded at fair value on a recurring basis at September 30, 2013, December 31, 2012 or September 30, 2012.
	Assets and Liabilities Recorded at Fair Value on a Nonrecurring Basis
	The Corporation does not record loans held for investment at fair value on a recurring basis. However, from time to time, a loan is considered impaired and an allocation of the allowance (valuation allowance) may be established or a portion of the loan is charged off. Loans for which it is probable that payment of interest and principal will not be made in accordance with the contractual terms of the loan agreement are considered impaired. The fair value of impaired loans is estimated using one of several methods, including the loan’s observable market price, the fair value of the collateral or the present value of the expected future cash flows discounted at the loan’s effective interest rate. Those impaired loans not requiring a valuation allowance represent loans for which the fair value of the expected repayments or collateral exceed the remaining carrying amount of such loans. Impaired loans where a valuation allowance is established or a portion of the loan is charged off based on the fair value of collateral are subject to nonrecurring fair value measurement and require classification in the fair value hierarchy. The Corporation records impaired loans as Level 3 valuations as there is generally no observable market price or independent appraised value, or management determines the fair value of the collateral is further impaired below the appraised value. When management determines the fair value of the collateral is further impaired below appraised value, discount factors ranging between 70% and 80% of the appraised value are used depending on the nature of the collateral and the age of the most recent appraisal.
	Goodwill is subject to impairment testing on an annual basis. The assessment of goodwill for impairment requires a significant degree of judgment. In the event the assessment indicates that it is more-likely-than-not that the fair value is less than the carrying value, the asset is considered impaired and recorded at fair value. Goodwill that is impaired and subject to nonrecurring fair value measurements is a Level 3 valuation. At September 30, 2013, December 31, 2012 and September 30, 2012, no goodwill was impaired, and therefore, goodwill was not recorded at fair value on a nonrecurring basis.
	Other intangible assets consist of core deposit intangible assets and MSRs. These items are both recorded at fair value when initially recorded. Subsequently, core deposit intangible assets are amortized primarily on an accelerated basis over periods ranging from ten to fifteen years and are subject to impairment testing whenever events or changes in circumstances indicate that the carrying amount exceeds the fair value of the asset. If core deposit intangible asset impairment is identified, the Corporation classifies impaired core deposit intangible assets subject to nonrecurring fair value measurements as Level 3 valuations. The fair value of MSRs is initially estimated using a model that calculates the net present value of estimated future cash flows using various assumptions, including prepayment speeds, the discount rate and servicing costs. If the valuation model reflects a value less than the carrying value, MSRs are adjusted to fair value, as determined by the model, through a valuation allowance. The Corporation classifies MSRs subject to nonrecurring fair value measurements as Level 3 valuations. At September 30, 2013, December 31, 2012 and September 30, 2012, there was no impairment identified for core deposit intangible assets or MSRs and, therefore, no other intangible assets were recorded at fair value on a nonrecurring basis.
	The carrying amounts for other real estate (ORE) and repossessed assets (RA) are reported in the consolidated statements of financial position under “Interest receivable and other assets.” ORE and RA include real estate and other types of assets repossessed by the Corporation. ORE and RA are recorded at the lower of cost or fair value upon the transfer of a loan to ORE or RA and, subsequently, ORE and RA continue to be measured and carried at the lower of cost or fair value. Fair value is based upon independent market prices, appraised values of the property or management’s estimation of the value of the property. The Corporation records ORE and RA as Level 3 valuations as management generally determines that the fair value of the property is impaired below the appraised value. When management determines the fair value of the property is further impaired below appraised value, discount factors ranging between 70% and 75% of the appraised value are used depending on the nature of the property and the age of the most recent appraisal.
	Disclosure of Nonrecurring Basis Fair Value Measurements
	For assets measured at fair value on a nonrecurring basis, quantitative disclosures about fair value measurements for each major category of assets were as follows:
		Fair Value Measurements – Nonrecurring Basis
		Quoted Prices				Significant				Significant				Total
		In Active				Other				Unobservable
		Markets for				Observable				Inputs
		Identical				Inputs				(Level 3)
		Assets				(Level 2)
		(Level 1)
		(In thousands)
30-Sep-13
Impaired originated loans		$	—			$	—			$	39,535			$	39,535
Other real estate/repossessed assets		—				—				12,033				12,033
Total		$	—			$	—			$	51,568			$	51,568
31-Dec-12
Impaired originated loans		$	—			$	—			$	51,694			$	51,694
Other real estate/repossessed assets		—				—				18,469				18,469
Total		$	—			$	—			$	70,163			$	70,163
30-Sep-12
Impaired originated loans		$	—			$	—			$	53,905			$	53,905
Other real estate/repossessed assets		—				—				19,467				19,467
Total		$	—			$	—			$	73,372			$	73,372
There were no liabilities recorded at fair value on a nonrecurring basis at September 30, 2013, December 31, 2012 and September 30, 2012.
Disclosures about Fair Value of Financial Instruments
GAAP requires disclosures about the estimated fair value of the Corporation's financial instruments, including those financial assets and liabilities that are not measured and reported at fair value on a recurring or nonrecurring basis. However, the method of estimating fair value for certain financial instruments, such as loans, that are not required to be measured on a recurring or nonrecurring basis, as prescribed by ASC Topic 820, Fair Value Measurements and Disclosures, does not incorporate the exit-price concept of fair value. The Corporation utilized the fair value hierarchy in computing the fair values of its financial instruments. In cases where quoted market prices were not available, the Corporation employed present value methods using unobservable inputs requiring management's judgment to estimate the fair values of its financial instruments, which are considered Level 3 valuations. These Level 3 valuations are affected by the assumptions made and, accordingly, do not necessarily indicate amounts that could be realized in a current market exchange. It is also the Corporation's general practice and intent to hold the majority of its financial instruments until maturity and, therefore, the Corporation does not expect to realize the estimated amounts disclosed.
The methodologies for estimating the fair value of financial assets and financial liabilities on a recurring or nonrecurring basis are discussed above. At September 30, 2013, December 31, 2012 and September 30, 2012, the estimated fair values of cash and cash equivalents, interest receivable and interest payable approximated their carrying values at those dates. The methodologies for other financial assets and financial liabilities follow.
Fair value measurement for investment securities — available-for-sale that are not measured at fair value on a recurring basis previously consisted of fixed-rate cumulative preferred stock issued by a bank holding company under the U.S. Government’s Troubled Asset Relief Program (TARP) with no maturity date and was based on cost. This preferred stock was not traded on a public exchange and did not have a readily determinable fair value. Accordingly, the Corporation recorded this preferred stock as a cost-method asset as prescribed by ASC Topic 325-20, Cost Method Investments. The issuer redeemed this preferred stock during the second quarter of 2013. Because no impairment indicators were present at December 31, 2012 or September 30, 2012, the Corporation was not required to estimate the fair value of this preferred stock.
Fair value measurement for investment securities — held-to-maturity is based upon quoted prices, if available. If quoted prices are not available, fair values are measured using independent pricing models or other model-based valuation techniques that include market inputs such as benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data and industry and economic events. Fair value measurements using Level 2 valuations of investment securities — held-to-maturity include the majority of the Corporation's investment securities issued by state and political subdivisions. Level 3 valuations include certain securities issued by state and political subdivisions and trust preferred investment securities. After reviewing the assumptions used to measure the fair value for its trust preferred investment securities, the Corporation transferred its trust preferred investment securities with a fair value of $6.2 million at September 30, 2013 from nonrecurring Level 2 assets to nonrecurring Level 3 assets during the second quarter of 2013.
Fair value measurements of nonmarketable equity securities, which consisted of Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock, are based on their redeemable value, which is cost. The market for these securities is restricted to the issuer of the stock and subject to impairment evaluation. It is not practicable to determine the fair value of these securities within the fair value hierarchy due to the restrictions placed on their transferability.
Loans held-for-sale are carried at fair value, as the Corporation elected the fair value option on these loans. The fair values of loans held-for-sale are based on the market price for similar loans sold in the secondary market, and therefore, are classified as Level 2 valuations.
The fair value of variable interest rate loans that reprice regularly with changes in market interest rates are based on carrying values. The fair values for fixed interest rate loans are estimated using discounted cash flow analyses, using the Corporation’s interest rates currently being offered for loans with similar terms to borrowers of similar credit quality. The resulting fair value amounts are adjusted to estimate the impact of changes in the credit quality of borrowers after the loans were originated. The fair value measurements for loans are Level 3 valuations.
The fair values of deposit accounts without defined maturities, such as interest- and noninterest-bearing checking, savings and money market accounts, are equal to the amounts payable on demand. Fair value measurements for fixed-interest rate time deposits with defined maturities are based on the discounted value of contractual cash flows, using the Corporation’s interest rates currently being offered for deposits of similar maturities, and are Level 3 valuations. The fair values for variable-interest rate time deposits with defined maturities approximate their carrying amounts.
Short-term borrowings consist of securities sold under agreements to repurchase. Fair value measurements for short-term borrowings are based on the present value of future estimated cash flows using current interest rates offered to the Corporation for debt with similar terms and are Level 2 valuations.
Fair value measurements for FHLB advances are estimated based on the present value of future estimated cash flows using current interest rates offered to the Corporation for debt with similar terms and are Level 2 valuations.
The Corporation’s unused commitments to extend credit, standby letters of credit and loan commitments have no carrying amount and have been estimated to have no realizable fair value. Historically, a majority of the unused commitments to extend credit have not been drawn upon and, generally, the Corporation does not receive fees in connection with these commitments other than standby letter of credit fees, which are not significant.
Fair value measurements have not been made for items that are not defined by GAAP as financial instruments, including such items as the value of the Corporation’s Wealth Management department and the value of the Corporation’s core deposit base. The Corporation believes it is impractical to estimate a representative fair value for these types of assets, even though management believes they add significant value to the Corporation.
A summary of carrying amounts and estimated fair values of the Corporation’s financial instruments included in the consolidated statements of financial position was as follows:
		Level in Fair Value Measurement		30-Sep-13								31-Dec-12						30-Sep-12
		Hierarchy		Carrying				Fair				Carrying				Fair		Carrying		Fair
				Amount				Value				Amount				Value		Amount		Value
				(In thousands)
Assets:
Cash and cash equivalents		Level 1		$	493,110			$	493,110			$	656,135			$	656,135	$	438,720	$	438,720
Investment securities:
Available-for-sale		Level 2		705,146				705,146				582,054				582,054		641,823		641,823
Available-for-sale		NA		—				—				4,755				4,755		4,755		4,755
Held-to-maturity		Level 2		272,079				269,616				229,977				229,922		213,536		215,185
Held-to-maturity		Level 3		10,500				6,250				—				—		8,000		8,000
Nonmarketable equity securities		NA		25,572				25,572				25,572				25,572		25,572		25,572
Loans held-for-sale		Level 2		7,907				7,907				17,665				17,665		15,075		15,075
Net loans		Level 3		4,441,139				4,446,796				4,083,244				4,093,880		3,934,465		3,951,313
Interest receivable		Level 2		16,359				16,359				14,933				14,933		16,868		16,868
Liabilities:
Deposits without defined maturities		Level 2		$	3,842,148			$	3,842,148			$	3,448,886			$	3,448,886	$	3,185,654	$	3,185,654
Time deposits		Level 3		1,349,157				1,359,739				1,472,557				1,489,072		1,413,218		1,432,493
Interest payable		Level 2		1,009				1,009				1,501				1,501		1,603		1,603
Short-term borrowings		Level 2		357,595				357,595				310,463				310,463		311,471		311,471
FHLB advances		Level 2		—				—				34,289				34,835		37,237		37,971

Earnings_Per_Common_Share

Earnings Per Common Share	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Earnings Per Common Share	'
	Earnings Per Common Share
	Basic earnings per common share for the Corporation is computed by dividing net income by the weighted average number of common shares outstanding during the period. Basic earnings per common share excludes any dilutive effect of common stock equivalents.
	Diluted earnings per common share for the Corporation is computed by dividing net income by the sum of the weighted average number of common shares outstanding and the dilutive effect of common stock equivalents using the treasury stock method. Average shares of common stock for diluted net income per common share include shares to be issued upon the exercise of stock options granted under the Corporation’s share-based compensation plans, restricted stock units that may be converted to stock, stock to be issued under the deferred stock compensation plan for non-employee directors and stock to be issued under the stock purchase plan for non-employee advisory directors. For any period in which a net loss is recorded, the assumed exercise of stock options, restricted stock units that may be converted to stock and stock to be issued under the deferred stock compensation plan and the stock purchase plan would have an anti-dilutive impact on the net loss per common share and thus are excluded in the diluted earnings per common share calculation.
	The following summarizes the numerator and denominator of the basic and diluted earnings per common share computations:
		Three Months Ended September 30,				Nine Months Ended September 30,
		2013		2012		2013		2012
		(In thousands, except per share data)
	Numerator for both basic and diluted earnings per common share, net income	$	14,993	$	13,106	$	42,430	$	39,346
	Denominator for basic earnings per common share, weighted average common shares outstanding	27,870		27,498		27,642		27,490
	Weighted average common stock equivalents	167		90		144		78
	Denominator for diluted earnings per common share	28,037		27,588		27,786		27,568
	Basic earnings per common share	$	0.54	$	0.48	$	1.54	$	1.43
	Diluted earnings per common share	0.53		0.48		1.53		1.43
	The average number of exercisable employee stock option awards outstanding that were “out-of-the-money,” whereby the option exercise price per share exceeded the market price per share and, therefore, were not included in the computation of diluted earnings per common share because they would have been anti-dilutive totaled 308,009 and 611,605 for the three months ended September 30, 2013 and 2012, respectively, and 377,847 and 618,703 for the nine months ended September 30, 2013 and 2012, respectively.

ShareBased_Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Share-Based Compensation	'
	Share-Based Compensation
	The Corporation maintains a share-based compensation plan under which it periodically grants share-based awards, which consist of stock options and restricted stock units, for a fixed number of shares to certain officers of the Corporation. The fair value of share-based awards is recognized as compensation expense over the requisite service or performance period. During the three-month periods ended September 30, 2013 and 2012, share-based compensation expense related to stock options and restricted stock units totaled $0.8 million and $0.5 million, respectively. During the nine-month periods ended September 30, 2013 and 2012, share-based compensation expense related to stock options and restricted stock units totaled $2.1 million and $1.3 million, respectively.
	During the nine-month period ended September 30, 2013, the Corporation granted options to purchase 244,219 shares of common stock and 71,429 restricted stock units to certain officers. At September 30, 2013, there were 674,140 shares of common stock available for future grants under the share-based compensation plan.
	Stock Options
	A summary of activity for the Corporation’s stock options as of and for the nine months ended September 30, 2013 is presented below:
			Non-Vested						Stock Options Outstanding
			Stock Options Outstanding
			Number of		Weighted-		Weighted-		Number of		Weighted-
			Options		Average		Average		Options		Average
					Exercise		Grant Date				Exercise
					Price		Fair Value				Price
					Per Share						Per Share
	Outstanding at January 1, 2013		314,765		$	23.03	$	6.92	997,222		$	27.24
	Granted		244,219		25.14		7.4		244,219		25.14
	Exercised		—		—		—		(87,842	)	22.84
	Vested		(126,682	)	22.96		6.93		—		—
	Forfeited/expired		(17,961	)	23.34		6.98		(19,086	)	24.07
	Outstanding at September 30, 2013		414,341		$	24.28	$	7.19	1,134,513		$	27.19
	Exercisable/vested at September 30, 2013								720,172		$	28.86
	The weighted-average remaining contractual terms were 5.7 years for all outstanding stock options and 3.8 years for exercisable stock options at September 30, 2013. The intrinsic value of all outstanding in-the-money stock options and exercisable in-the-money stock options was $3.3 million and $1.8 million, respectively, at September 30, 2013. The aggregate intrinsic values of outstanding and exercisable options at September 30, 2013 were calculated based on the closing market price of the Corporation’s common stock on September 30, 2013 of $27.92 per share less the exercise price. Options with intrinsic values less than zero, or “out-of-the-money” options, were not included in the aggregate intrinsic value reported.
	At September 30, 2013, unrecognized compensation expense related to stock options totaled $2.4 million and is expected to be recognized over a remaining weighted average period of 2.0 years.
	The fair value of the stock options granted during the nine months ended September 30, 2013 was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions.
	Expected dividend yield	3.5		%
	Risk-free interest rate	1.34		%
	Expected stock price volatility	42.1		%
	Expected life of options – in years	7
	Weighted average fair value of options granted	$	7.4
	Restricted Stock Units
	In addition to stock options, during the nine months ended September 30, 2013, the Corporation granted restricted stock performance units and restricted stock service-based units (collectively referred to as restricted stock units) to certain officers. The restricted stock performance units vest based on the Corporation achieving certain performance target levels. The restricted stock performance units are eligible to vest from 0.25x to 1.5x the number of units originally granted depending on which, if any, of the performance target levels are met. However, if the minimum performance target level is not achieved, no shares will become vested or be issued for that respective year’s restricted stock performance units. The restricted stock service-based units vest upon satisfaction of a service condition. Upon achievement of the performance target level and/or satisfaction of a service condition, if applicable, the restricted stock units are converted into shares of the Corporation’s common stock on a one-to-one basis. Compensation expense related to restricted stock units is recognized over the expected requisite performance or service period, as applicable.
	A summary of the activity for restricted stock units as of and for the nine months ended September 30, 2013 is presented below:
			Number of		Weighted-
			Units		Average
					Grant Date
					Fair Value
					Per Unit
	Outstanding at January 1, 2013		156,510		$	20.83
	Granted		71,429		23.41
	Converted into shares of common stock		(36,172	)	22.47
	Forfeited/expired		(3,330	)	21.67
	Outstanding at September 30, 2013		188,437		$	21.48
	At September 30, 2013, unrecognized compensation expense related to restricted stock unit awards totaled $2.7 million and is expected to be recognized over a remaining weighted average period of 2.2 years.

Pension_and_Other_Postretireme

Pension and Other Postretirement Benefit Plans	9 Months Ended
	Sep. 30, 2013
Compensation and Retirement Disclosure [Abstract]	'
Pension and Other Postretirement Benefit Plans	'
	Pension and Other Postretirement Benefit Plans
	The components of net periodic benefit cost (income) for the Corporation’s qualified and nonqualified pension plans and nonqualified postretirement benefit plan are as follows:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
		(In thousands)
	Defined Benefit Pension Plans
	Service cost	$	326		$	304		$	976		$	910
	Interest cost	1,166			1,214			3,500			3,644
	Expected return on plan assets	(1,949		)	(1,731		)	(5,845		)	(5,194		)
	Amortization of prior service credit	—			—			(1		)	(1		)
	Amortization of unrecognized net loss	946			614			2,838			1,843
	Net periodic benefit cost	$	489		$	401		$	1,468		$	1,202
	Postretirement Benefit Plan
	Service cost	$	5		$	—		$	14		$	—
	Interest cost	36			37			108			110
	Amortization of prior service cost (credit)	27			(75		)	233			(225		)
	Amortization of unrecognized net gain	(18		)	(7		)	(55		)	(21		)
	Net periodic benefit cost (income)	$	50		$	(45	)	$	300		$	(136	)
	The Corporation’s pension plan does not have a contribution requirement in 2013. The Corporation made a voluntary $15.0 million contribution to the pension plan during the first quarter of 2013. The discount rate used to compute the Corporation's pension plan expense for 2013 is 4.08%.
	401(k) Savings Plan expense for the Corporation’s match of participants’ base compensation contributions and a 4% of eligible pay contribution to certain employees who are not grandfathered under the pension plan was $0.9 million and $0.8 million for the three months ended September 30, 2013 and 2012, respectively, and $2.7 million and $2.3 million for the nine months ended September 30, 2013 and 2012, respectively.

Financial_Guarantees

Financial Guarantees	9 Months Ended
	Sep. 30, 2013
Guarantees [Abstract]	'
Financial Guarantees	'
	Financial Guarantees
	In the normal course of business, the Corporation is a party to financial instruments containing credit risk that are not required to be reflected in the consolidated statements of financial position. For the Corporation, these financial instruments are financial and performance standby letters of credit. The Corporation has risk management policies to identify, monitor and limit exposure to credit risk. To mitigate credit risk for these financial guarantees, the Corporation generally determines the need for specific covenant, guarantee and collateral requirements on a case-by-case basis, depending on the nature of the financial instrument and the customer’s creditworthiness. At September 30, 2013, December 31, 2012 and September 30, 2012, the Corporation had $48 million, $43 million and $43 million, respectively, of outstanding financial and performance standby letters of credit that expire in five years or less. The majority of these standby letters of credit are collateralized. The Corporation determined that there were no potential losses from standby letters of credit at September 30, 2013, December 31, 2012 and September 30, 2012.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Nature of Operations	'
	Nature of Operations
	Chemical Financial Corporation (Corporation) operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operates through one commercial bank, Chemical Bank. Chemical Bank operates within the State of Michigan as a state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of four regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the bank’s geographical market areas. The products and services offered by the regional banking units, through branch banking offices, are generally consistent throughout the Corporation, as is the pricing of those products and services. The marketing of products and services throughout the Corporation’s regional banking units is generally uniform, as many of the markets served by the regional banking units overlap. The distribution of products and services is uniform throughout the Corporation’s regional banking units and is achieved primarily through retail branch banking offices, automated teller machines and electronically accessed banking products.
	The Corporation’s primary sources of revenue are interest from its loan products and investment securities, service charges and fees from customer deposit accounts and wealth management revenue.
Basis of Presentation	'
	Basis of Presentation
	The accompanying unaudited consolidated financial statements of the Corporation and its subsidiaries have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, the consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s consolidated financial statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2012. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments believed necessary to present fairly the financial condition and results of operations of the Corporation for the periods presented. Operating results for the nine months ended September 30, 2013 are not necessarily indicative of the results that may be expected for the year ending December 31, 2013.
Use of Estimates	'
	Use of Estimates
	Management makes estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying footnotes. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, expected cash flows from acquired loans, fair value amounts related to business combinations, pension expense, income taxes, goodwill impairment and those assets that require fair value measurement. Actual results could differ from these estimates.
Reclassifications	'
	Reclassifications
	Certain amounts in the consolidated statements of income for the three and nine months ended September 30, 2012 have been reclassified to conform with the 2013 presentation. Such reclassifications had no effect on the Corporation's assets, liabilities, shareholders' equity or net income.
Originated Loans	'
	Originated Loans
	Originated loans include all of the Corporation's portfolio loans, excluding loans acquired on April 30, 2010 in the acquisition of O.A.K. Financial Corporation (OAK). Originated loans also include loans acquired as part of the Corporation's branch acquisition on December 7, 2012, as these loans were performing and were considered high-quality loans in accordance with the Corporation's credit underwriting standards at that date. Originated loans are stated at their principal amount outstanding, net of unearned income, charge-offs and unamortized deferred fees and costs. Loan interest income is recognized on the accrual basis. Deferred loan fees and costs are amortized over the loan term based on the level-yield method. Net loan commitment fees are deferred and amortized into fee income on a straight-line basis over the commitment period.
	The past due status of a loan is based on the loan’s contractual terms. A loan is placed in nonaccrual status (accrual of interest is discontinued) when principal or interest is past due 90 days or more (except for a loan that is secured by residential real estate, which is transferred to nonaccrual status at 120 days past due), unless the loan is both well-secured and in the process of collection, or earlier when, in the opinion of management, there is sufficient reason to doubt the collectibility of principal or interest. Interest previously accrued, but not collected, is reversed and charged against interest income at the time the loan is placed in nonaccrual status. Subsequent receipts of interest while a loan is in nonaccrual status are recorded as a reduction of principal. Loans are returned to accrual status when principal and interest payments are brought current, payments have been received consistently for a period of time (generally six months) and collectibility is no longer in doubt.
Loans Acquired in a Business Combination	'
	Loans Acquired in a Business Combination
	Loans acquired in a business combination (acquired loans) consist of loans acquired on April 30, 2010 in the acquisition of OAK. Acquired loans were recorded at fair value at the date of acquisition, without a carryover of the associated allowance for loan losses related to these loans, through a fair value discount that was, in part, attributable to deterioration in credit quality. The estimate of expected credit losses was determined based on due diligence performed by executive and senior officers of the Corporation, with assistance from third-party consultants. The fair value discount was recorded as a reduction of the acquired loans’ outstanding principal balances in the consolidated statement of financial position at the acquisition date.
	The Corporation accounts for acquired loans, which are recorded at fair value at acquisition, in accordance with Accounting Standards Codifications (ASC) Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality (ASC 310-30). ASC 310-30 allows investors to aggregate loans acquired into loan pools that have common risk characteristics and thereby use a composite interest rate and expectation of cash flows expected to be collected for the loan pools. Under the provisions of ASC 310-30, the Corporation aggregated acquired loans into 14 pools based upon common risk characteristics, including types of loans, commercial type loans with similar risk grades and whether loans were performing or nonperforming. A pool is considered a single unit of accounting for purposes of applying the guidance prescribed in ASC 310-30. A loan will be removed from a pool of acquired loans only if the loan is sold, foreclosed, paid off or written off, and will be removed from the pool at the carrying value. If an individual loan is removed from a pool of loans, the difference between its relative carrying amount and the cash, fair value of the collateral, or other assets received would not affect the effective yield used to recognize the accretable difference on the remaining pool. The Corporation estimated the cash flows expected to be collected over the life of the pools of loans at acquisition, and estimates expected cash flows quarterly thereafter, based on a set of assumptions including expectations as to default rates, prepayment rates and loss severities. The Corporation must make numerous assumptions, interpretations and judgments using internal and third-party credit quality information to determine whether it is probable that the Corporation will be able to collect all contractually required payments. This is a point in time assessment and inherently subjective due to the nature of the available information and judgment involved.
	The calculation of the fair value of the acquired loan pools entails estimating the amount and timing of cash flows attributable to both principal and interest expected to be collected on such loan pools and then discounting those cash flows at market interest rates. The excess of a loan pool's expected cash flows at the acquisition date over its estimated fair value is referred to as the "accretable yield," which is recognized into interest income over the estimated remaining life of the loan pool on a level-yield basis. The difference between a loan pool's contractually required principal and interest payments at the acquisition date and the cash flows expected to be collected at the acquisition date is referred to as the "nonaccretable difference," which includes an estimate of future credit losses expected to be incurred over the estimated life of the loan pool and interest payments that are not expected to be collected. Decreases to the expected cash flows in each loan pool in subsequent periods will require the Corporation to record a provision for loan losses. Improvements in expected cash flows in each loan pool in subsequent periods will result in reversing a portion of the nonaccretable difference, which is then classified as part of the accretable yield and subsequently recognized into interest income over the estimated remaining life of the loan pool.
Loans Modified Under Troubled Debt Restructurings	'
	Loans Modified Under Troubled Debt Restructurings
	Loans modified under troubled debt restructurings (TDRs) involve granting a concession to a borrower who is experiencing financial difficulty. Concessions generally include modifications to original loan terms, including changes to a loan’s payment schedule or interest rate, which generally would not otherwise be considered. The Corporation’s loans reported as TDRs consist of originated loans that continue to accrue interest at the loan’s original interest rate as the Corporation expects to collect the remaining principal and interest on the loan. The Corporation’s loans reported as TDRs do not include loans that are in a nonaccrual status that have been modified by the Corporation due to the borrower experiencing financial difficulty and for which a concession has been granted, as the Corporation does not expect to collect the full amount of principal and interest owed from the borrower on these modified loans. The interest income recognized on TDRs may include accretion of an identified impairment at the time of modification which is attributable to a temporary reduction in the borrower’s interest rate. At the time of modification, a TDR is reported as a nonperforming loan (nonperforming TDR) until a six-month payment history of principal and interest payments, in accordance with the terms of the loan modification, is sustained, at which time the Corporation moves the loan to a performing status (performing TDR). All TDRs are accounted for as impaired loans and are included in the Corporation’s analysis of the allowance for loan losses. A TDR that has been renewed for a borrower who is no longer experiencing financial difficulty and which yields a market rate of interest at the time of a renewal is no longer reported as a TDR in the first quarter following the calendar year in which the renewal took place.
	Loans in the Corporation’s commercial loan portfolio (comprised of commercial, commercial real estate, real estate construction and land development loans) that meet the definition of a TDR generally consist of loans where the Corporation has allowed borrowers to defer scheduled principal payments and make interest-only payments for a specified period of time at the stated interest rate of the original loan agreement or reduced payments due to a moderate extension of the loan’s contractual term. The Corporation does not expect to incur a loss on these loans based on its assessment of the borrowers’ expected cash flows, as the pre- and post-modification effective yields are approximately the same for these loans. Accordingly, no additional provision for loan losses has been recognized related to these loans. Since no loss is expected to be incurred on these loans, the loans accrue interest at the loan’s contractual interest rate. These loans are individually evaluated for impairment and transferred to nonaccrual status if it is probable that any remaining principal and interest payments due on the loans will not be collected in accordance with the modified terms of the loans.
	Loans in the Corporation’s consumer loan portfolio (comprised of residential mortgage, consumer installment and home equity loans) that meet the definition of a TDR generally include a concession that reduces a borrower’s monthly payments by decreasing the interest rate charged on the loan for a specified period of time (generally 24 months) under a formal modification agreement. The Corporation recognizes an additional provision for loan losses related to impairment on these loans on an individual basis based on the present value of expected future cash flows discounted at the loan’s original effective interest rate. These loans continue to accrue interest at the loan's effective interest rate, which consists of contractual interest under the terms of the modification agreement in addition to an adjustment for the accretion of computed impairment. These loans are moved to nonaccrual status if they become 90 days past due as to principal or interest, or sooner if conditions warrant.
Impaired Loans	'
	Impaired Loans
	A loan is defined to be impaired when it is probable that payment of principal and interest will not be made in accordance with the original contractual terms of the loan agreement. Impaired loans include nonaccrual loans, TDRs (nonperforming and performing) and acquired loans that were not performing in accordance with original contractual terms. Impaired loans are accounted for at the lower of the present value of expected cash flows discounted at the loan's effective interest rate or the estimated fair value of the collateral, if the loan is collateral dependent. When the present value of expected cash flows or the fair value of collateral of an impaired loan in the originated loan portfolio is less than the amount of unpaid principal outstanding on the loan, the principal balance of the loan is reduced to its carrying value through either an allocation of the allowance for loan losses or a partial charge-off of the loan balance.
Nonperforming Loans	'
	Nonperforming Loans
	Nonperforming loans are comprised of loans for which the accrual of interest has been discontinued (nonaccrual loans), accruing originated loans contractually past due 90 days or more as to interest or principal payments and nonperforming TDRs.
Allowance for Loan Losses	'
	Allowance for Loan Losses
	The allowance for loan losses (allowance) is presented as a reserve against loans. The allowance represents management’s assessment of probable loan losses inherent in the Corporation’s loan portfolio.
	Management’s evaluation of the adequacy of the allowance is based on a continuing review of the loan portfolio, actual loan loss experience, the underlying value of the collateral, risk characteristics of the loan portfolio, the level and composition of nonperforming loans, the financial condition of the borrowers, the balance of the loan portfolio, loan growth, economic conditions, employment levels in the Corporation’s local markets, and special factors affecting specific business sectors. The Corporation maintains formal policies and procedures to monitor and control credit risk. Management evaluates the allowance on a quarterly basis in an effort to ensure the level is appropriate to absorb probable losses inherent in the loan portfolio.
	The allowance provides for probable losses that have been identified with specific customer relationships and for probable losses believed to be incurred in the remainder of the originated loan portfolio, but that have not been specifically identified. The Corporation utilizes its own loss experience to estimate inherent losses on loans. Internal risk ratings are assigned to each loan in the commercial loan portfolio (commercial, commercial real estate, real estate construction and land development loans) at the time of approval and are subject to subsequent periodic reviews by senior management. The Corporation performs a detailed credit quality review quarterly on all loans greater than $0.25 million that have deteriorated below certain levels of credit risk and may allocate a specific portion of the allowance to such loans based upon this review. A portion of the allowance is allocated to the remaining loans by applying projected loss ratios, based on numerous factors. Projected loss ratios incorporate factors such as recent charge-off experience, trends with respect to adversely risk-rated loans in the commercial loan portfolio, trends with respect to past due and nonaccrual loans, changes in economic conditions and trends, changes in the value of underlying collateral and other credit risk factors. This evaluation involves a high degree of uncertainty.
	In determining the allowance and the related provision for loan losses, the Corporation considers four principal elements: (i) valuation allowances based upon probable losses identified during the review of impaired loans in the commercial loan portfolio, (ii) allocations established for adversely-rated loans in the commercial loan portfolio and nonaccrual residential mortgage, consumer installment and home equity loans, (iii) allocations, by loan classes, on all other loans based principally on a five-year historical loan loss experience and loan loss trends and (iv) an unallocated allowance based on the imprecision in the overall allowance methodology for loans collectively evaluated for impairment.
	Although the Corporation allocates portions of the allowance to specific loans and loan types, the entire allowance attributable to originated loans is available for any loan losses that occur in the originated portfolio. Loans that are deemed not collectible are charged off and reduce the allowance. The provision for loan losses and recoveries on loans previously charged off increase the allowance. Collection efforts may continue and recoveries may occur after a loan is charged off.
	Acquired loans are aggregated into pools based upon common risk characteristics. An allowance may be recorded related to an acquired loan pool if it experiences a decrease in expected cash flows, as compared to those projected at the acquisition date. On a quarterly basis, the expected future cash flow of each pool is estimated based on various factors, including changes in property values of collateral dependent loans, default rates, loss severities and prepayment speeds. Decreases in estimates of expected cash flows within a pool generally result in a charge to the provision for loan losses and a corresponding increase in the allowance allocated to acquired loans for the particular pool. Increases in estimates of expected cash flows within a pool generally result in a reduction in the allowance allocated to acquired loans for the particular pool, if applicable, and then an adjustment to the accretable yield for the pool, which will increase amounts recognized in interest income in subsequent periods.
	Various regulatory agencies, as an integral part of their examination process, periodically review the allowance. Such agencies may require additions to the allowance, based on their judgment, reflecting information available to them at the time of their examinations.
Fair Value Measurements	'
	Fair Value Measurements
	Fair value for assets and liabilities measured at fair value on a recurring or nonrecurring basis refers to the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants in the market in which the reporting entity transacts such sales or transfers based on the assumptions market participants would use when pricing an asset or liability. Assumptions are developed based on prioritizing information within a fair value hierarchy that gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data, such as the reporting entity’s own data.
	The Corporation may choose to measure eligible items at fair value at specified election dates. Unrealized gains and losses on items for which the fair value measurement option has been elected are reported in earnings at each subsequent reporting date. The fair value option (i) may be applied instrument by instrument, with certain exceptions, allowing the Corporation to record identical financial assets and liabilities at fair value or by another measurement basis permitted under GAAP, (ii) is irrevocable (unless a new election date occurs) and (iii) is applied only to entire instruments and not to portions of instruments. At September 30, 2013, December 31, 2012 and September 30, 2012, the Corporation elected the fair value option on all of its loans held-for-sale. The Corporation has not elected the fair value option for any other financial assets or liabilities.
Share-Based Compensation	'
	Share-Based Compensation
	The Corporation grants stock options, stock awards, restricted stock performance units and restricted stock service-based units to certain executive and senior management employees. The Corporation accounts for share-based compensation expense using the modified-prospective transition method. Under that method, compensation expense is recognized for stock options based on the estimated grant date fair value as computed using the Black-Scholes option pricing model and the probability of issuance. The Corporation accounts for stock awards based on the closing stock price of the Corporation's common stock on the date of the award. The fair values of both stock options and stock awards are recognized as compensation expense on a straight-line basis over the requisite service period. The Corporation accounts for restricted stock performance units based on the closing stock price of the Corporation's common stock on the date of grant, discounted by the present value of estimated future dividends to be declared over the requisite performance or service period. The fair value of restricted stock performance units is recognized as compensation expense over the expected requisite performance period, or requisite service period for awards with multiple performance and service conditions. The Corporation accounts for restricted stock service-based units based on the closing stock price of the Corporation's common stock on the date of grant, as these awards accrue dividend equivalents equal to the amount of any cash dividends that would have been payable to a shareholder owning the number of shares of the Corporation's common stock represented by the restricted stock service-based units. The fair value of the restricted stock service-based units is recognized as compensation expense over the requisite service period.
	Cash flows realized from the tax benefits of exercised stock option awards that result from actual tax deductions that are in excess of the recorded tax benefits related to the compensation expense recognized for those options (excess tax benefits) are classified as financing activities on the consolidated statements of cash flows.
Income and Other Taxes	'
	Income and Other Taxes
	The Corporation is subject to the income and other tax laws of the United States, the State of Michigan and other states where nexus has been created. These laws are complex and are subject to different interpretations by the taxpayer and the various taxing authorities. In determining the provision for income and other taxes, management must make judgments and estimates about the application of these inherently complex laws, related regulations and case law. In the process of preparing the Corporation’s tax returns, management attempts to make reasonable interpretations of enacted tax laws. These interpretations are subject to challenge by the tax authorities upon audit or to reinterpretation based on management’s ongoing assessment of facts and evolving case law.
	On a quarterly basis, management assesses the reasonableness of its estimated annual effective federal tax rate based upon its current best estimate of taxable income and the applicable taxes expected for the full year. Deferred tax assets and liabilities are reassessed on a quarterly basis, including the need for a valuation allowance for deferred tax assets.
	Uncertain income tax positions are evaluated to determine whether it is more-likely-than-not that a tax position will be sustained upon examination based on the technical merits of the tax position. If a tax position is more-likely-than-not to be sustained, a tax benefit is recognized for the amount that is greater than 50% likely to be realized. Reserves for contingent income tax liabilities attributable to unrecognized tax benefits associated with uncertain tax positions are reviewed quarterly for adequacy based upon developments in tax law and the status of audits or examinations. The Corporation had no contingent income tax liabilities recorded at September 30, 2013, December 31, 2012 or September 30, 2012. The tax periods open to examination by the Internal Revenue Service include the calendar years ended December 31, 2012, 2011 and 2010.
Shareholders' Equity	'
	Shareholders’ Equity
	Common Stock Repurchase Programs
	From time to time, the board of directors of the Corporation approves common stock repurchase programs allowing management to repurchase shares of the Corporation’s common stock in the open market. The repurchased shares are available for later reissuance in connection with potential future stock dividends, the Corporation’s dividend reinvestment plan, employee benefit plans and other general corporate purposes. Under these programs, the timing and actual number of shares subject to repurchase are at the discretion of management and are contingent on a number of factors, including the projected parent company cash flow requirements and the Corporation’s market price per share.
	In January 2008, the board of directors of the Corporation authorized the repurchase of up to 500,000 shares of the Corporation’s common stock under a stock repurchase program. In November 2011, the board of directors of the Corporation reaffirmed the stock buy-back authorization with the qualification that the shares may only be repurchased if the share price is below the tangible book value per share of the Corporation’s common stock at the time of the repurchase. Since the January 2008 authorization, no shares have been repurchased. At September 30, 2013, there were 500,000 remaining shares available for repurchase under the Corporation’s stock repurchase programs.
	Preferred Stock
	On April 20, 2009, the shareholders of the Corporation authorized the board of directors of the Corporation to issue up to 200,000 shares of preferred stock in connection with either an acquisition by the Corporation of an entity that has shares of preferred stock issued and outstanding pursuant to any program established by the United States government or participation by the Corporation in any program established by the United States government. At September 30, 2013, no shares of preferred stock were issued and outstanding.
Legal Matters	'
	Legal Matters
	The Corporation and Chemical Bank are subject to certain legal actions arising in the ordinary course of business. In the opinion of management, after consultation with legal counsel, the ultimate disposition of these matters is not expected to have a material adverse effect on the consolidated financial condition or results of operations of the Corporation.
Adopted Accounting Pronouncements	'
	Adopted Accounting Pronouncements
	In February 2013, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2013-02, Comprehensive Income (Topic 220): Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income (ASU 2013-02). Under ASU 2013-02, an entity is required to provide information about the amounts reclassified out of Accumulated Other Comprehensive Income (AOCI) by component. In addition, an entity is required to present, either on the face of the financial statements or in the notes, significant amounts reclassified out of AOCI by the respective line items of net income, but only if the amount reclassified is required to be reclassified in its entirety in the same reporting period. For amounts that are not required to be reclassified in their entirety to net income, an entity is required to cross-reference to other disclosures that provide additional details about those amounts. ASU 2013-02 does not change the requirements for reporting net income or other comprehensive income in the financial statements. ASU 2013-02 is effective for interim and annual periods beginning on or after December 15, 2012. The adoption of ASU 2013-02 as of January 1, 2013 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
Pending Accounting Pronouncements	'
	Pending Accounting Pronouncements
	In February 2013, the FASB issued ASU 2013-04, Liabilities (Topic 405): Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation is Fixed at the Reporting Date (ASU 2013-04). ASU 2013-04 provides guidance in relation to the recognition, measurement and disclosure of obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date. ASU 2013-04 is effective for interim and annual periods beginning after December 15, 2013 and should be applied retrospectively for all periods presented for those obligations resulting from joint and several liability arrangements that exist at the beginning of the fiscal year of adoption. The adoption of ASU 2013-04 is not expected to have a material impact on the Corporation's consolidated financial condition or results of operations.

Acquisitions_Tables

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
Activity for accretable yield includes contractually due interest of acquired loans	'
	Activity for the accretable yield, which includes contractually due interest for acquired loans that have been renewed or extended since the date of acquisition and continue to be accounted for in loan pools in accordance with ASC 310-30, follows:
			Nine Months Ended
			September 30,
			2013			2012
			(In thousands)
	Balance at beginning of period		$	49,390		$	68,305
	Additions (reductions)*		(997		)	6,237
	Accretion recognized in interest income		(13,235		)	(18,543		)
	Reclassification from nonaccretable difference		125			—
	Balance at end of period		$	35,283		$	55,999
	*	Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.

Investment_Securities_Tables

Investment Securities (Tables)	9 Months Ended
	Sep. 30, 2013
Investments, Debt and Equity Securities [Abstract]	'
Available-for-sale Securities	'
	The following is a summary of the amortized cost and fair value of investment securities available-for-sale and investment securities held-to-maturity at September 30, 2013, December 31, 2012 and September 30, 2012:
		Investment Securities Available-for-Sale
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	30-Sep-13
	Government sponsored agencies	$	86,065	$	264	$	404	$	85,925
	State and political subdivisions	44,191		1,386		5		45,572
	Residential mortgage-backed securities	310,550		1,144		3,534		308,160
	Collateralized mortgage obligations	200,407		199		2,148		198,458
	Corporate bonds	65,053		583		202		65,434
	Preferred stock	1,389		208		—		1,597
	Total	$	707,655	$	3,784	$	6,293	$	705,146
	31-Dec-12
	Government sponsored agencies	$	97,529	$	241	$	213	$	97,557
	State and political subdivisions	47,663		2,302		—		49,965
	Residential mortgage-backed securities	96,320		3,100		9		99,411
	Collateralized mortgage obligations	262,790		984		182		263,592
	Corporate bonds	69,788		546		539		69,795
	Preferred stock	6,144		345		—		6,489
	Total	$	580,234	$	7,518	$	943	$	586,809
	30-Sep-12
	Government sponsored agencies	$	101,576	$	182	$	266	$	101,492
	State and political subdivisions	49,707		2,538		7		52,238
	Residential mortgage-backed securities	101,709		3,543		16		105,236
	Collateralized mortgage obligations	297,960		1,392		274		299,078
	Corporate bonds	82,219		509		622		82,106
	Preferred stock	6,144		284		—		6,428
	Total	$	639,315	$	8,448	$	1,185	$	646,578
Held-to-maturity Securities	'
		Investment Securities Held-to-Maturity
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	30-Sep-13
	State and political subdivisions	$	272,079	$	5,978	$	8,441	$	269,616
	Trust preferred securities	10,500		—		4,250		6,250
	Total	$	282,579	$	5,978	$	12,691	$	275,866
	31-Dec-12
	State and political subdivisions	$	219,477	$	8,087	$	3,367	$	224,197
	Trust preferred securities	10,500		—		4,775		5,725
	Total	$	229,977	$	8,087	$	8,142	$	229,922
	30-Sep-12
	State and political subdivisions	$	211,036	$	8,661	$	1,712	$	217,985
	Trust preferred securities	10,500		—		5,300		5,200
	Total	$	221,536	$	8,661	$	7,012	$	223,185
Amortized cost and fair value of debt securities by contractual maturity	'
	The following is a summary of the amortized cost and fair value of investment securities at September 30, 2013, by maturity, for both available-for-sale and held-to-maturity investment securities. The maturities of residential mortgage-backed securities and collateralized mortgage obligations are based on scheduled principal payments. The maturities of all other debt securities are based on final contractual maturity.
		30-Sep-13
		Amortized		Fair Value
		Cost
		(In thousands)
	Investment Securities Available-for-Sale:
	Due in one year or less	$	91,500	$	91,946
	Due after one year through five years	117,337		118,555
	Due after five years through ten years	426,031		422,118
	Due after ten years	71,398		70,930
	Preferred stock	1,389		1,597
	Total	$	707,655	$	705,146
	Investment Securities Held-to-Maturity:
	Due in one year or less	$	42,112	$	42,179
	Due after one year through five years	114,020		115,646
	Due after five years through ten years	74,316		74,353
	Due after ten years	52,131		43,688
	Total	$	282,579	$	275,866
Summary of continuous unrealized loss position of securities	'
	The following schedule summarizes information for both available-for-sale and held-to-maturity investment securities with gross unrealized losses at September 30, 2013, December 31, 2012 and September 30, 2012, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position.
		Less Than 12 Months				12 Months or More				Total
		Fair		Gross		Fair		Gross		Fair		Gross
		Value		Unrealized		Value		Unrealized		Value		Unrealized
				Losses				Losses				Losses
		(In thousands)
	30-Sep-13
	Government sponsored agencies	$	43,816	$	223	$	14,395	$	181	$	58,211	$	404
	State and political subdivisions	120,232		6,918		30,915		1,528		151,147		8,446
	Residential mortgage-backed securities	267,495		3,532		40		2		267,535		3,534
	Collateralized mortgage obligations	129,049		1,617		15,302		531		144,351		2,148
	Corporate bonds	9,926		85		19,883		117		29,809		202
	Trust preferred securities	—		—		6,250		4,250		6,250		4,250
	Total	$	570,518	$	12,375	$	86,785	$	6,609	$	657,303	$	18,984
	31-Dec-12
	Government sponsored agencies	$	46,103	$	213	$	—	$	—	$	46,103	$	213
	State and political subdivisions	70,675		2,257		8,046		1,110		78,721		3,367
	Residential mortgage-backed securities	273		1		1,305		8		1,578		9
	Collateralized mortgage obligations	19,331		10		36,835		172		56,166		182
	Corporate bonds	4,747		253		34,707		286		39,454		539
	Trust preferred securities	—		—		5,725		4,775		5,725		4,775
	Total	$	141,129	$	2,734	$	86,618	$	6,351	$	227,747	$	9,085
	30-Sep-12
	Government sponsored agencies	$	39,729	$	248	$	8,808	$	18	$	48,537	$	266
	State and political subdivisions	69,841		1,711		1,533		8		71,374		1,719
	Residential mortgage-backed securities	32		1		19,704		15		19,736		16
	Collateralized mortgage obligations	12,036		45		47,066		229		59,102		274
	Corporate bonds	19,469		531		24,900		91		44,369		622
	Trust preferred securities	—		—		5,200		5,300		5,200		5,300
	Total	$	141,107	$	2,536	$	107,211	$	5,661	$	248,318	$	8,197

Loans_Tables

Loans (Tables)	9 Months Ended
	Sep. 30, 2013
Receivables [Abstract]	'
Summary of loans under portfolio	'
	A summary of loans follows:
		September 30,				December 31,				September 30,
		2013				2012				2012
		(In thousands)
	Commercial loan portfolio:
	Commercial	$	1,128,122			$	1,002,722			$	951,938
	Commercial real estate	1,215,631				1,161,861				1,117,073
	Real estate construction	78,361				62,689				56,071
	Land development	23,673				37,548				34,811
	Subtotal	2,445,787				2,264,820				2,159,893
	Consumer loan portfolio:
	Residential mortgage	942,777				883,835				880,295
	Consumer installment	622,040				546,036				538,412
	Home equity	512,067				473,044				440,559
	Subtotal	2,076,884				1,902,915				1,859,266
	Total loans	$	4,522,671			$	4,167,735			$	4,019,159
Recorded investment of loans in the commercial loan portfolio by risk rating categories	'
	The following schedule presents the recorded investment of loans in the commercial loan portfolio by risk rating categories at September 30, 2013, December 31, 2012 and September 30, 2012:
		Commercial				Real Estate				Real Estate				Land				Total
						Commercial				Construction				Development
		(In thousands)
	30-Sep-13
	Originated Portfolio:
	Risk Grades 1-5	$	974,903			$	963,394			$	64,210			$	7,760			$	2,010,267
	Risk Grade 6	16,439				37,572				58				1,063				55,132
	Risk Grade 7	37,644				30,969				1,337				4,870				74,820
	Risk Grade 8	9,753				28,186				183				2,954				41,076
	Risk Grade 9	2,056				437				—				—				2,493
	Subtotal	1,040,795				1,060,558				65,788				16,647				2,183,788
	Acquired Portfolio:
	Risk Grades 1-5	82,648				141,234				12,573				4,604				241,059
	Risk Grade 6	2,620				4,837				—				—				7,457
	Risk Grade 7	992				7,847				—				—				8,839
	Risk Grade 8	1,067				1,155				—				2,422				4,644
	Risk Grade 9	—				—				—				—				—
	Subtotal	87,327				155,073				12,573				7,026				261,999
	Total	$	1,128,122			$	1,215,631			$	78,361			$	23,673			$	2,445,787
	31-Dec-12
	Originated Portfolio:
	Risk Grades 1-5	$	827,112			$	846,901			$	47,847			$	15,010			$	1,736,870
	Risk Grade 6	38,066				45,261				59				497				83,883
	Risk Grade 7	16,831				26,343				—				6,367				49,541
	Risk Grade 8	12,540				33,345				1,217				4,184				51,286
	Risk Grade 9	2,061				4,315				—				—				6,376
	Subtotal	896,610				956,165				49,123				26,058				1,927,956
	Acquired Portfolio:
	Risk Grades 1-5	93,281				188,499				13,566				8,419				303,765
	Risk Grade 6	8,225				5,900				—				237				14,362
	Risk Grade 7	2,169				9,677				—				—				11,846
	Risk Grade 8	2,437				1,620				—				2,834				6,891
	Risk Grade 9	—				—				—				—				—
	Subtotal	106,112				205,696				13,566				11,490				336,864
	Total	$	1,002,722			$	1,161,861			$	62,689			$	37,548			$	2,264,820
	30-Sep-12
	Originated Portfolio:
	Risk Grades 1-5	$	772,555			$	793,237			$	37,346			$	12,348			$	1,615,486
	Risk Grade 6	33,819				38,880				18				1,092				73,809
	Risk Grade 7	17,091				30,971				—				5,313				53,375
	Risk Grade 8	14,790				38,369				933				5,731				59,823
	Risk Grade 9	427				2,942				—				—				3,369
	Subtotal	838,682				904,399				38,297				24,484				1,805,862
	Acquired Portfolio:
	Risk Grades 1-5	97,308				192,903				17,774				7,556				315,541
	Risk Grade 6	10,899				7,006				—				—				17,905
	Risk Grade 7	2,107				11,672				—				—				13,779
	Risk Grade 8	2,942				1,093				—				2,771				6,806
	Risk Grade 9	—				—				—				—				—
	Subtotal	113,256				212,674				17,774				10,327				354,031
	Total	$	951,938			$	1,117,073			$	56,071			$	34,811			$	2,159,893
Recorded investment of loans in the consumer loan portfolio based on the credit risk profile of loans in a performing and nonperforming status	'
	The following schedule presents the recorded investment of loans in the consumer loan portfolio based on loans in a performing status and loans in a nonperforming status at September 30, 2013, December 31, 2012 and September 30, 2012:
		Residential Mortgage				Consumer				Home Equity				Total
						Installment								Consumer
		(In thousands)
	30-Sep-13
	Originated Loans:
	Performing	$	918,931			$	619,346			$	475,439			$	2,013,716
	Nonperforming	11,850				665				3,709				16,224
	Subtotal	930,781				620,011				479,148				2,029,940
	Acquired Loans:
	Performing	11,918				2,029				32,737				46,684
	Nonperforming	78				—				182				260
	Subtotal	11,996				2,029				32,919				46,944
	Total	$	942,777			$	622,040			$	512,067			$	2,076,884
	31-Dec-12
	Originated Loans:
	Performing	$	854,882			$	543,339			$	429,734			$	1,827,955
	Nonperforming	14,988				739				3,502				19,229
	Subtotal	869,870				544,078				433,236				1,847,184
	Acquired Loans:
	Performing	13,843				1,958				39,637				55,438
	Nonperforming	122				—				171				293
	Subtotal	13,965				1,958				39,808				55,731
	Total	$	883,835			$	546,036			$	473,044			$	1,902,915
	30-Sep-12
	Originated Loans:
	Performing	$	849,385			$	535,277			$	395,411			$	1,780,073
	Nonperforming	15,640				962				4,010				20,612
	Subtotal	865,025				536,239				399,421				1,800,685
	Acquired Loans:
	Performing	14,928				2,173				40,874				57,975
	Nonperforming	342				—				264				606
	Subtotal	15,270				2,173				41,138				58,581
	Total	$	880,295			$	538,412			$	440,559			$	1,859,266
Summary of nonperforming loans	'
	A summary of nonperforming loans follows:
		September 30,				December 31,				September 30,
		2013				2012				2012
		(In thousands)
	Nonaccrual loans:
	Commercial	$	11,809			$	14,601			$	15,217
	Commercial real estate	28,623				37,660				41,311
	Real estate construction	183				1,217				933
	Land development	2,954				4,184				5,731
	Residential mortgage	8,029				10,164				11,307
	Consumer installment	665				739				876
	Home equity	3,023				2,733				2,949
	Total nonaccrual loans	55,286				71,298				78,324
	Accruing loans contractually past due 90 days or more as to interest or principal payments:
	Commercial	281				—				273
	Commercial real estate	—				87				247
	Real estate construction	—				—				—
	Land development	—				—				—
	Residential mortgage	692				1,503				431
	Consumer installment	—				—				—
	Home equity	686				769				1,147
	Total accruing loans contractually past due 90 days or more as to interest or principal payments	1,659				2,359				2,098
	Nonperforming TDRs:
	Commercial loan portfolio	15,744				13,876				6,553
	Consumer loan portfolio	3,129				3,321				3,902
	Total nonperforming TDRs	18,873				17,197				10,455
	Total nonperforming loans	$	75,818			$	90,854			$	90,877
Schedule of Impaired loans by classes	'
	The following schedule presents impaired loans by classes of loans at September 30, 2013, December 31, 2012 and September 30, 2012:
		Recorded				Unpaid				Related
		Investment				Principal				Valuation
						Balance				Allowance
		(In thousands)
	30-Sep-13
	Impaired loans with a valuation allowance:
	Commercial	$	5,059			$	5,803			$	1,857
	Commercial real estate	6,684				7,901				1,651
	Real estate construction	183				253				33
	Land development	517				653				97
	Residential mortgage	17,731				17,731				585
	Subtotal	30,174				32,341				4,223
	Impaired loans with no related valuation allowance:
	Commercial	21,543				25,642				—
	Commercial real estate	43,178				57,256				—
	Real estate construction	133				133				—
	Land development	9,095				13,347				—
	Residential mortgage	8,029				8,029				—
	Consumer installment	665				665				—
	Home equity	3,023				3,023				—
	Subtotal	85,666				108,095				—
	Total impaired loans:
	Commercial	26,602				31,445				1,857
	Commercial real estate	49,862				65,157				1,651
	Real estate construction	316				386				33
	Land development	9,612				14,000				97
	Residential mortgage	25,760				25,760				585
	Consumer installment	665				665				—
	Home equity	3,023				3,023				—
	Total	$	115,840			$	140,436			$	4,223
	31-Dec-12
	Impaired loans with a valuation allowance:
	Commercial	$	6,368			$	6,818			$	1,966
	Commercial real estate	17,267				17,607				5,359
	Real estate construction	171				171				75
	Land development	254				254				50
	Residential mortgage	18,901				18,901				658
	Subtotal	42,961				43,751				8,108
	Impaired loans with no related valuation allowance:
	Commercial	23,230				27,959				—
	Commercial real estate	37,223				48,531				—
	Real estate construction	1,046				1,116				—
	Land development	10,867				15,112				—
	Residential mortgage	10,164				10,164				—
	Consumer installment	739				739				—
	Home equity	2,733				2,733				—
	Subtotal	86,002				106,354				—
	Total impaired loans:
	Commercial	29,598				34,777				1,966
	Commercial real estate	54,490				66,138				5,359
	Real estate construction	1,217				1,287				75
	Land development	11,121				15,366				50
	Residential mortgage	29,065				29,065				658
	Consumer installment	739				739				—
	Home equity	2,733				2,733				—
	Total	$	128,963			$	150,105			$	8,108
		Recorded				Unpaid				Related
		Investment				Principal				Valuation
						Balance				Allowance
		(In thousands)
	30-Sep-12
	Impaired loans with a valuation allowance:
Commercial	$	6,743			$	7,357			$	2,240
Commercial real estate	19,694				22,593				5,344
Real estate construction	127				127				43
Land development	2,800				2,800				383
Residential mortgage	15,958				15,958				649
Subtotal	45,322				48,835				8,659
Impaired loans with no related valuation allowance:
Commercial	19,768				24,517				—
Commercial real estate	36,225				48,187				—
Real estate construction	806				806				—
Land development	7,723				10,903				—
Residential mortgage	14,907				14,907				—
Consumer installment	876				876				—
Home equity	2,949				2,949				—
Subtotal	83,254				103,145				—
Total impaired loans:
Commercial	26,511				31,874				2,240
Commercial real estate	55,919				70,780				5,344
Real estate construction	933				933				43
Land development	10,523				13,703				383
Residential mortgage	30,865				30,865				649
Consumer installment	876				876				—
Home equity	2,949				2,949				—
Total	$	128,576			$	151,980			$	8,659
Schedule presents information related to impaired loans	'
	The following schedule presents information related to impaired loans for the three and nine months ended September 30, 2013 and 2012:
		Three Months Ended September 30, 2013								Nine Months Ended September 30, 2013
		Average				Interest  Income				Average				Interest  Income
		Recorded				Recognized				Recorded				Recognized
		Investment				While on				Investment				While on
						Impaired Status								Impaired Status
		(In thousands)
	Commercial	$	27,025			$	215			$	26,894			$	633
	Commercial real estate	50,266				284				53,482				984
	Real estate construction	414				2				395				7
	Land development	9,615				79				10,470				261
	Residential mortgage	25,826				278				27,216				847
	Consumer installment	632				—				666				—
	Home equity	3,091				—				2,977				—
	Total	$	116,869			$	858			$	122,100			$	2,732
		Three Months Ended September 30, 2012								Nine Months Ended September 30, 2012
		Average				Interest  Income				Average				Interest  Income
		Recorded				Recognized				Recorded				Recognized
		Investment				While on				Investment				While on
						Impaired Status								Impaired Status
		(In thousands)
	Commercial	$	28,683			$	149			$	27,684			$	602
	Commercial real estate	54,524				212				59,063				642
	Real estate construction	912				—				470				—
	Land development	10,582				71				8,869				216
	Residential mortgage	33,652				288				37,861				1,031
	Consumer installment	909				—				1,222				—
	Home equity	2,940				—				2,910				—
	Total	$	132,202			$	720			$	138,079			$	2,491
Schedule representing the aging status of the recorded investment in loans by classes	'
	The following schedule presents the aging status of the recorded investment in loans by classes of loans at September 30, 2013, December 31, 2012 and September 30, 2012:
		31-60				61-89				Accruing				Non-accrual				Total				Current		Total
		Days				Days				Loans				Loans				Past Due						Loans
		Past Due				Past Due				Past Due
										90 Days
										or More
		(In thousands)
	30-Sep-13
	Originated Portfolio:
	Commercial	$	7,833			$	1,542			$	281			$	11,809			$	21,465			$	1,019,330	$	1,040,795
	Commercial real estate	6,533				2,274				—				28,623				37,430				1,023,128		1,060,558
	Real estate construction	90				5,385				—				183				5,658				60,130		65,788
	Land development	187				—				—				2,954				3,141				13,506		16,647
	Residential mortgage	1,739				76				692				8,029				10,536				920,245		930,781
	Consumer installment	2,980				350				—				665				3,995				616,016		620,011
	Home equity	2,344				434				686				3,023				6,487				472,661		479,148
	Total	$	21,706			$	10,061			$	1,659			$	55,286			$	88,712			$	4,125,016	$	4,213,728
	Acquired Portfolio:
	Commercial	$	67			$	—			$	1,574			$	—			$	1,641			$	85,686	$	87,327
	Commercial real estate	439				—				3,355				—				3,794				151,279		155,073
	Real estate construction	—				—				—				—				—				12,573		12,573
	Land development	—				—				2,422				—				2,422				4,604		7,026
	Residential mortgage	264				—				77				—				341				11,655		11,996
	Consumer installment	3				1				—				—				4				2,025		2,029
	Home equity	389				79				182				—				650				32,269		32,919
	Total	$	1,162			$	80			$	7,610			$	—			$	8,852			$	300,091	$	308,943
		31-60				61-89				Accruing				Non-accrual				Total				Current		Total
		Days				Days				Loans				Loans				Past Due						Loans
		Past Due				Past Due				Past Due
										90 Days
										or More
		(In thousands)
	31-Dec-12
	Originated Portfolio:
	Commercial	$	3,999			$	730			$	—			$	14,601			$	19,330			$	877,280	$	896,610
	Commercial real estate	5,852				2,089				87				37,660				45,688				910,477		956,165
	Real estate construction	—				—				—				1,217				1,217				47,906		49,123
	Land development	—				—				—				4,184				4,184				21,874		26,058
	Residential mortgage	3,161				55				1,503				10,164				14,883				854,987		869,870
	Consumer installment	2,415				378				—				739				3,532				540,546		544,078
	Home equity	1,618				427				769				2,733				5,547				427,689		433,236
	Total	$	17,045			$	3,679			$	2,359			$	71,298			$	94,381			$	3,680,759	$	3,775,140
	Acquired Portfolio:
	Commercial	$	—			$	—			$	2,834			$	—			$	2,834			$	103,278	$	106,112
	Commercial real estate	287				15				3,139				—				3,441				202,255		205,696
	Real estate construction	—				—				—				—				—				13,566		13,566
	Land development	—				—				2,834				—				2,834				8,656		11,490
	Residential mortgage	123				—				122				—				245				13,720		13,965
	Consumer installment	10				—				—				—				10				1,948		1,958
	Home equity	205				—				170				—				375				39,433		39,808
	Total	$	625			$	15			$	9,099			$	—			$	9,739			$	382,856	$	392,595
	30-Sep-12
	Originated Portfolio:
	Commercial	$	9,707			$	1,374			$	273			$	15,217			$	26,571			$	812,111	$	838,682
	Commercial real estate	4,929				1,660				247				41,311				48,147				856,252		904,399
	Real estate construction	—				—				—				933				933				37,364		38,297
	Land development	48				—				—				5,731				5,779				18,705		24,484
	Residential mortgage	3,208				97				431				11,307				15,043				849,982		865,025
	Consumer installment	3,299				470				—				876				4,645				531,594		536,239
	Home equity	1,543				730				1,147				2,949				6,369				393,052		399,421
	Total	$	22,734			$	4,331			$	2,098			$	78,324			$	107,487			$	3,499,060	$	3,606,547
	Acquired Portfolio:
	Commercial	$	—			$	15			$	3,356			$	—			$	3,371			$	109,885	$	113,256
Commercial real estate	1,262				—				2,390				—				3,652				209,022		212,674
Real estate construction	—				—				—				—				—				17,774		17,774
Land development	—				—				3,038				—				3,038				7,289		10,327
Residential mortgage	80				—				343				—				423				14,847		15,270
Consumer installment	18				—				—				—				18				2,155		2,173
Home equity	138				39				264				—				441				40,697		41,138
Total	$	1,498			$	54			$	9,391			$	—			$	10,943			$	401,669	$	412,612
Schedule of Corporation's TDRs	'
	The following schedule presents the Corporation’s loans reported as TDRs at September 30, 2013, December 31, 2012 and September 30, 2012:
		Performing				Nonperforming				Total
		(In thousands)
	30-Sep-13
	Commercial loan portfolio	$	19,469			$	15,744			$	35,213
	Consumer loan portfolio	14,602				3,129				17,731
	Total	$	34,071			$	18,873			$	52,944
	31-Dec-12
	Commercial loan portfolio	$	15,789			$	13,876			$	29,665
	Consumer loan portfolio	15,580				3,321				18,901
	Total	$	31,369			$	17,197			$	48,566
	30-Sep-12
	Commercial loan portfolio	$	14,750			$	6,553			$	21,303
	Consumer loan portfolio	15,656				3,902				19,558
	Total	$	30,406			$	10,455			$	40,861
Schedule providing information on performing and nonperforming TDRs	'
	The following schedule provides information on loans reported as performing and nonperforming TDRs that were either modified during the three and nine months ended September 30, 2013 and 2012 or modified during a previous period and transfered from nonaccrual status during the three and nine months ended September 30, 2013 and 2012:
		Three Months Ended September 30, 2013											Nine Months Ended September 30, 2013
		Number			Pre-				Post-				Number			Pre-				Post-
		of  Loans			Modification				Modification				of  Loans			Modification				Modification
					Recorded				Recorded							Recorded				Recorded
					Investment				Investment							Investment				Investment
		(Dollars in thousands)
	Commercial loan portfolio:
	Commercial	2			$	352			$	352			11			$	3,370			$	3,370
	Commercial real estate	3			2,100				2,100				16			8,701				8,701
	Land development	—			—				—				3			637				637
	Subtotal – commercial loan portfolio	5			2,452				2,452				30			12,708				12,708
	Consumer loan portfolio (residential mortgage)	19			1,647				1,604				48			3,534				3,435
	Total	24			$	4,099			$	4,056			78			$	16,242			$	16,143
		Three Months Ended September 30, 2012											Nine Months Ended September 30, 2012
		Number			Pre-				Post-				Number			Pre-				Post-
		of  Loans			Modification				Modification				of  Loans			Modification				Modification
					Recorded				Recorded							Recorded				Recorded
					Investment				Investment							Investment				Investment
		(Dollars in thousands)
	Commercial loan portfolio:
	Commercial	9			$	665			$	665			19			$	3,891			$	3,891
	Commercial real estate	8			1,426				1,426				19			5,264				5,264
	Land development	—			—				—				1			1,638				1,638
	Subtotal – commercial loan portfolio	17			2,091				2,091				39			10,793				10,793
	Consumer loan portfolio (residential mortgage)	15			1,352				1,301				65			7,083				6,872
	Total	32			$	3,443			$	3,392			104			$	17,876			$	17,665
Troubled debt restructurings on financing receivables with defaults payment	'
	The following schedule includes loans reported as performing and nonperforming TDRs at September 30, 2013 and 2012, and TDRs that were transferred to nonaccrual status during the three and nine months ended September 30, 2013 and 2012, for which there was a payment default during the three and nine months ended September 30, 2013 and 2012, whereby the borrower was past due with respect to principal and/or interest for 90 days or more, and the loan became a TDR during the twelve-month period prior to the default:
		Three Months Ended September 30, 2013							Nine Months Ended September 30, 2013
		Number of			Principal Balance at End of Period				Number of			Principal Balance at End of Period
		Loans							Loans
		(Dollars in thousands)
	Commercial loan portfolio:
	Commercial	1			$	748			2			$	1,182
	Commercial real estate	4			2,833				4			2,833
	Subtotal – commercial loan portfolio	5			3,581				6			4,015
	Consumer loan portfolio (residential mortgage)	4			109				7			478
	Total	9			$	3,690			13			$	4,493
		Three Months Ended September 30, 2012							Nine Months Ended September 30, 2012
		Number of			Principal Balance at End of Period				Number of			Principal Balance at End of Period
		Loans							Loans
		(Dollars in thousands)
	Commercial loan portfolio:
	Commercial	2			$	1,240			3			$	1,300
	Commercial real estate	3			2,457				5			3,293
	Subtotal – commercial loan portfolio	5			3,697				8			4,593
	Consumer loan portfolio (residential mortgage)	1			742				5			1,126
	Total	6			$	4,439			13			$	5,719
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'
	The following schedule presents, by loan portfolio segment, the changes in the allowance for the three and nine months ended September 30, 2013 and details regarding the balance in the allowance and the recorded investment in loans at September 30, 2013 by impairment evaluation method.
		Commercial				Consumer				Unallocated				Total
		Loan				Loan
		Portfolio				Portfolio
		(In thousands)
	Changes in allowance for loan losses for the three months ended September 30, 2013:
	Beginning balance	$	47,780			$	28,745			$	5,659			$	82,184
	Provision for loan losses	2,810				2,165				(1,975		)		3,000
	Charge-offs	(2,637		)		(1,793		)		—				(4,430		)
	Recoveries	374				404				—				778
	Ending balance	$	48,327			$	29,521			$	3,684			$	81,532
	Changes in allowance for loan losses for the nine months ended September 30, 2013:
	Beginning balance	$	49,975			$	29,333			$	5,183			$	84,491
	Provision for loan losses	5,815				4,684				(1,499		)		9,000
	Charge-offs	(9,374		)		(5,891		)		—				(15,265		)
	Recoveries	1,911				1,395				—				3,306
	Ending balance	$	48,327			$	29,521			$	3,684			$	81,532
	Allowance for loan losses balance at September 30, 2013 attributable to:
	Loans individually evaluated for impairment	$	3,638			$	585			$	—			$	4,223
	Loans collectively evaluated for impairment	44,689				28,436				3,684				76,809
	Loans acquired with deteriorated credit quality	—				500				—				500
	Total	$	48,327			$	29,521			$	3,684			$	81,532
	Recorded investment (loan balance) at September 30, 2013:
	Loans individually evaluated for impairment	$	78,782			$	17,731			$	—			$	96,513
	Loans collectively evaluated for impairment	2,105,006				2,012,209				—				4,117,215
	Loans acquired with deteriorated credit quality	261,999				46,944				—				308,943
	Total	$	2,445,787			$	2,076,884			$	—			$	4,522,671
	The following schedule presents, by loan portfolio segment, details regarding the balance in the allowance and the recorded investment in loans at December 31, 2012 by impairment evaluation method.
		Commercial				Consumer				Unallocated				Total
		Loan				Loan
		Portfolio				Portfolio
		(In thousands)
	Allowance for loan losses balance at December 31, 2012 attributable to:
	Loans individually evaluated for impairment	$	7,450			$	658			$	—			$	8,108
	Loans collectively evaluated for impairment	42,525				28,175				5,183				75,883
	Loans acquired with deteriorated credit quality	—				500				—				500
	Total	$	49,975			$	29,333			$	5,183			$	84,491
	Recorded investment (loan balance) at December 31, 2012:
	Loans individually evaluated for impairment	$	87,327			$	18,901			$	—			$	106,228
	Loans collectively evaluated for impairment	1,840,629				1,828,283				—				3,668,912
	Loans acquired with deteriorated credit quality	336,864				55,731				—				392,595
	Total	$	2,264,820			$	1,902,915			$	—			$	4,167,735
	The following schedule presents, by loan portfolio segment, the changes in the allowance for the three and nine months ended September 30, 2012 and details regarding the balance in the allowance and the recorded investment in loans at September 30, 2012 by impairment evaluation method.
		Commercial				Consumer				Unallocated				Total
		Loan				Loan
		Portfolio				Portfolio
		(In thousands)
	Changes in allowance for loan losses for the three months ended September 30, 2012:
	Beginning balance	$	53,759			$	29,784			$	3,168			$	86,711
	Provision for loan losses	2,365				1,765				370				4,500
	Charge-offs	(4,754		)		(2,842		)		—				(7,596		)
	Recoveries	460				619				—				1,079
	Ending balance	$	51,830			$	29,326			$	3,538			$	84,694
	Changes in allowance for loan losses for the nine months ended September 30, 2012:
	Beginning balance	$	55,645			$	29,166			$	3,522			$	88,333
	Provision for loan losses	6,003				7,481				16				13,500
	Charge-offs	(11,330		)		(8,985		)		—				(20,315		)
	Recoveries	1,512				1,664				—				3,176
	Ending balance	$	51,830			$	29,326			$	3,538			$	84,694
	Allowance for loan losses balance at September 30, 2012 attributable to:
	Loans individually evaluated for impairment	$	8,010			$	649			$	—			$	8,659
	Loans collectively evaluated for impairment	43,820				28,177				3,538				75,535
	Loans acquired with deteriorated credit quality	—				500				—				500
Total	$	51,830			$	29,326			$	3,538			$	84,694
Recorded investment (loan balance) at September 30, 2012:
Loans individually evaluated for impairment	$	84,495			$	19,558			$	—			$	104,053
Loans collectively evaluated for impairment	1,721,367				1,781,127				—				3,502,494
Loans acquired with deteriorated credit quality	354,031				58,581				—				412,612
Total	$	2,159,893			$	1,859,266			$	—			$	4,019,159

Intangible_Assets_Tables

Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Net carrying value of intangible assets	'
	The following table shows the net carrying value of the Corporation’s intangible assets:
		September 30,			December 31,			September 30,
		2013			2012			2012
		(In thousands)
	Goodwill	$	120,164		$	120,164		$	113,414
	Other intangible assets:
	Core deposit intangible assets	$	10,466		$	11,910		$	6,777
	Mortgage servicing rights	3,399			3,478			3,466
	Total other intangible assets	$	13,865		$	15,388		$	10,243
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets	'
	The following table sets forth the carrying amount, accumulated amortization and amortization expense of core deposit intangible assets that are amortizable and arose from business combinations or other acquisitions:
		September 30,			December 31,			September 30,
		2013			2012			2012
		(In thousands)
	Gross original amount	$	18,659		$	18,659		$	26,468
	Accumulated amortization	8,193			6,749			19,691
	Carrying amount	$	10,466		$	11,910		$	6,777
	Amortization expense for the three months ended September 30	$	467					$	367
	Amortization expense for the nine months ended September 30	$	1,444					$	1,102
Net carrying value, fair value of MSRs and loans Corporation servicing for others	'
	The following shows the net carrying value and fair value of MSRs and the total loans that the Corporation is servicing for others:
		September 30,			December 31,			September 30,
		2013			2012			2012
		(In thousands)
	Net carrying value of MSRs	$	3,399		$	3,478		$	3,466
	Fair value of MSRs	$	6,839		$	4,716		$	4,277
	Loans serviced for others that have servicing rights capitalized	$	886,980		$	906,314		$	901,052
Activity for capitalized MSRs	'
	The following table shows the activity for capitalized MSRs:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
		(In thousands)
	Balance at beginning of period	$	3,421		$	3,463		$	3,478		$	3,593
	Additions	311			503			1,271			1,706
	Amortization	(333		)	(500		)	(1,350		)	(1,833		)
	Balance at end of period	$	3,399		$	3,466		$	3,399		$	3,466

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Loss (Tables)	9 Months Ended
	Sep. 30, 2013
Equity [Abstract]	'
Components of accumulated other comprehensive loss, net of related tax benefit/expense	'
	The components of accumulated other comprehensive loss, net of related tax benefit/expense, were as follows:
		September 30,			December 31,			September 30,
		2013			2012			2012
		(In thousands)
	Net unrealized gains (losses) on investment securities – available-for-sale, net of related tax expense (benefit) of $(878) at September 30, 2013, $2,301 at December 31, 2012 and $2,542 at September 30, 2012	$	(1,631	)	$	4,274		$	4,721
	Pension and other postretirement benefits adjustment, net of related tax benefit of $18,062 at September 30, 2013, $19,058 at December 31, 2012 and $14,876 at September 30, 2012	(33,544		)	(35,393		)	(27,627		)
	Accumulated other comprehensive loss	$	(35,175	)	$	(31,119	)	$	(22,906	)

Regulatory_Capital_Tables

Regulatory Capital (Tables)	9 Months Ended
	Sep. 30, 2013
Banking and Thrift [Abstract]	'
Corporation's and Chemical Bank's actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy	'
	The summary below compares the Corporation’s and Chemical Bank’s actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy:
		Actual				Minimum Required for Capital Adequacy Purposes				Required to be Well Capitalized Under Prompt Corrective Action Regulations
		Capital		Ratio		Capital		Ratio		Capital		Ratio
		Amount				Amount				Amount
		(Dollars in thousands)
	30-Sep-13
	Total Capital to Risk-Weighted Assets:
	Corporation	$	638,786	14.2	%	$	361,199	8	%	N/A		N/A
	Chemical Bank	568,626		12.6		360,617		8		$	450,771	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	582,039		12.9		180,600		4		N/A		N/A
	Chemical Bank	511,969		11.4		180,309		4		270,463		6
	Leverage Ratio:
	Corporation	582,039		10		232,972		4		N/A		N/A
	Chemical Bank	511,969		8.8		232,828		4		291,034		5
	31-Dec-12
	Total Capital to Risk-Weighted Assets:
	Corporation	$	552,171	13.2	%	$	334,140	8	%	N/A		N/A
	Chemical Bank	536,223		12.9		333,195		8		$	416,494	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	499,563		12		167,070		4		N/A		N/A
	Chemical Bank	483,761		11.6		166,598		4		249,896		6
	Leverage Ratio:
	Corporation	499,563		9.2		217,145		4		N/A		N/A
	Chemical Bank	483,761		8.9		216,784		4		270,980		5
	30-Sep-12
	Total Capital to Risk-Weighted Assets:
	Corporation	$	549,388	13.6	%	$	322,212	8	%	N/A		N/A
	Chemical Bank	537,467		13.4		321,585		8		$	401,982	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	498,618		12.4		161,106		4		N/A		N/A
	Chemical Bank	486,794		12.1		160,793		4		241,189		6
	Leverage Ratio:
	Corporation	498,618		9.4		211,670		4		N/A		N/A
	Chemical Bank	486,794		9.2		211,452		4		264,315		5

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Summary of assets measured at fair value on a recurring basis	'
	For assets measured at fair value on a recurring basis, quantitative disclosures about the fair value measurements for each major category of assets were as follows:
		Fair Value Measurements – Recurring Basis
		Quoted Prices				Significant				Significant				Total
		In Active				Other				Unobservable
		Markets for				Observable				Inputs
		Identical				Inputs				(Level 3)
		Assets				(Level 2)
		(Level 1)
		(In thousands)
	30-Sep-13
	Investment securities – available-for-sale:
	Government sponsored agencies	$	—			$	85,925			$	—			$	85,925
	State and political subdivisions	—				45,572				—				45,572
	Residential mortgage-backed securities	—				308,160				—				308,160
	Collateralized mortgage obligations	—				198,458				—				198,458
	Corporate bonds	—				65,434				—				65,434
	Preferred stock	—				1,597				—				1,597
	Total investment securities – available-for-sale	—				705,146				—				705,146
	Loans held-for-sale	—				7,907				—				7,907
	Total assets measured at fair value on a recurring basis	$	—			$	713,053			$	—			$	713,053
	31-Dec-12
	Investment securities – available-for-sale:
	Government sponsored agencies	$	—			$	97,557			$	—			$	97,557
	State and political subdivisions	—				49,965				—				49,965
	Residential mortgage-backed securities	—				99,411				—				99,411
	Collateralized mortgage obligations	—				263,592				—				263,592
	Corporate bonds	—				69,795				—				69,795
	Preferred stock	—				1,734				—				1,734
	Total investment securities – available-for-sale	—				582,054				—				582,054
	Loans held-for-sale	—				17,665				—				17,665
	Total assets measured at fair value on a recurring basis	$	—			$	599,719			$	—			$	599,719
	30-Sep-12
	Investment securities – available-for-sale:
	Government sponsored agencies	$	—			$	101,492			$	—			$	101,492
	State and political subdivisions	—				52,238				—				52,238
	Residential mortgage-backed securities	—				105,236				—				105,236
	Collateralized mortgage obligations	—				299,078				—				299,078
	Corporate bonds	—				82,106				—				82,106
	Preferred stock	—				1,673				—				1,673
	Total investment securities – available-for-sale	—				641,823				—				641,823
	Loans held-for-sale	—				15,075				—				15,075
	Total assets measured at fair value on a recurring basis	$	—			$	656,898			$	—			$	656,898
Summary of assets measured at fair value on a nonrecurring basis	'
	For assets measured at fair value on a nonrecurring basis, quantitative disclosures about fair value measurements for each major category of assets were as follows:
		Fair Value Measurements – Nonrecurring Basis
		Quoted Prices				Significant				Significant				Total
		In Active				Other				Unobservable
		Markets for				Observable				Inputs
		Identical				Inputs				(Level 3)
		Assets				(Level 2)
		(Level 1)
		(In thousands)
	30-Sep-13
	Impaired originated loans	$	—			$	—			$	39,535			$	39,535
	Other real estate/repossessed assets	—				—				12,033				12,033
	Total	$	—			$	—			$	51,568			$	51,568
	31-Dec-12
	Impaired originated loans	$	—			$	—			$	51,694			$	51,694
	Other real estate/repossessed assets	—				—				18,469				18,469
	Total	$	—			$	—			$	70,163			$	70,163
	30-Sep-12
	Impaired originated loans	$	—			$	—			$	53,905			$	53,905
	Other real estate/repossessed assets	—				—				19,467				19,467
	Total	$	—			$	—			$	73,372			$	73,372
Summary of carrying amounts and estimated fair values of the financial instruments	'
	A summary of carrying amounts and estimated fair values of the Corporation’s financial instruments included in the consolidated statements of financial position was as follows:
		Level in Fair Value Measurement		30-Sep-13								31-Dec-12						30-Sep-12
		Hierarchy		Carrying				Fair				Carrying				Fair		Carrying		Fair
				Amount				Value				Amount				Value		Amount		Value
				(In thousands)
	Assets:
	Cash and cash equivalents	Level 1		$	493,110			$	493,110			$	656,135			$	656,135	$	438,720	$	438,720
	Investment securities:
	Available-for-sale	Level 2		705,146				705,146				582,054				582,054		641,823		641,823
	Available-for-sale	NA		—				—				4,755				4,755		4,755		4,755
	Held-to-maturity	Level 2		272,079				269,616				229,977				229,922		213,536		215,185
	Held-to-maturity	Level 3		10,500				6,250				—				—		8,000		8,000
	Nonmarketable equity securities	NA		25,572				25,572				25,572				25,572		25,572		25,572
	Loans held-for-sale	Level 2		7,907				7,907				17,665				17,665		15,075		15,075
	Net loans	Level 3		4,441,139				4,446,796				4,083,244				4,093,880		3,934,465		3,951,313
	Interest receivable	Level 2		16,359				16,359				14,933				14,933		16,868		16,868
	Liabilities:
	Deposits without defined maturities	Level 2		$	3,842,148			$	3,842,148			$	3,448,886			$	3,448,886	$	3,185,654	$	3,185,654
	Time deposits	Level 3		1,349,157				1,359,739				1,472,557				1,489,072		1,413,218		1,432,493
	Interest payable	Level 2		1,009				1,009				1,501				1,501		1,603		1,603
	Short-term borrowings	Level 2		357,595				357,595				310,463				310,463		311,471		311,471
	FHLB advances	Level 2		—				—				34,289				34,835		37,237		37,971

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Numerator and denominator of the basic and diluted earnings per common share computations	'
	The following summarizes the numerator and denominator of the basic and diluted earnings per common share computations:
		Three Months Ended September 30,				Nine Months Ended September 30,
		2013		2012		2013		2012
		(In thousands, except per share data)
	Numerator for both basic and diluted earnings per common share, net income	$	14,993	$	13,106	$	42,430	$	39,346
	Denominator for basic earnings per common share, weighted average common shares outstanding	27,870		27,498		27,642		27,490
	Weighted average common stock equivalents	167		90		144		78
	Denominator for diluted earnings per common share	28,037		27,588		27,786		27,568
	Basic earnings per common share	$	0.54	$	0.48	$	1.54	$	1.43
	Diluted earnings per common share	0.53		0.48		1.53		1.43

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Summary of activity for Corporation's stock options	'
	A summary of activity for the Corporation’s stock options as of and for the nine months ended September 30, 2013 is presented below:
			Non-Vested						Stock Options Outstanding
			Stock Options Outstanding
			Number of		Weighted-		Weighted-		Number of		Weighted-
			Options		Average		Average		Options		Average
					Exercise		Grant Date				Exercise
					Price		Fair Value				Price
					Per Share						Per Share
	Outstanding at January 1, 2013		314,765		$	23.03	$	6.92	997,222		$	27.24
	Granted		244,219		25.14		7.4		244,219		25.14
	Exercised		—		—		—		(87,842	)	22.84
	Vested		(126,682	)	22.96		6.93		—		—
	Forfeited/expired		(17,961	)	23.34		6.98		(19,086	)	24.07
	Outstanding at September 30, 2013		414,341		$	24.28	$	7.19	1,134,513		$	27.19
	Exercisable/vested at September 30, 2013								720,172		$	28.86
Assumptions of Black-Scholes option pricing model	'
	The fair value of the stock options granted during the nine months ended September 30, 2013 was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions.
	Expected dividend yield	3.5		%
	Risk-free interest rate	1.34		%
	Expected stock price volatility	42.1		%
	Expected life of options – in years	7
	Weighted average fair value of options granted	$	7.4
Summary of activity for restricted stock performance units	'
	A summary of the activity for restricted stock units as of and for the nine months ended September 30, 2013 is presented below:
			Number of		Weighted-
			Units		Average
					Grant Date
					Fair Value
					Per Unit
	Outstanding at January 1, 2013		156,510		$	20.83
	Granted		71,429		23.41
	Converted into shares of common stock		(36,172	)	22.47
	Forfeited/expired		(3,330	)	21.67
	Outstanding at September 30, 2013		188,437		$	21.48

Pension_and_Other_Postretireme1

Pension and Other Postretirement Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2013
Compensation and Retirement Disclosure [Abstract]	'
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan	'
	The components of net periodic benefit cost (income) for the Corporation’s qualified and nonqualified pension plans and nonqualified postretirement benefit plan are as follows:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
		(In thousands)
	Defined Benefit Pension Plans
	Service cost	$	326		$	304		$	976		$	910
	Interest cost	1,166			1,214			3,500			3,644
	Expected return on plan assets	(1,949		)	(1,731		)	(5,845		)	(5,194		)
	Amortization of prior service credit	—			—			(1		)	(1		)
	Amortization of unrecognized net loss	946			614			2,838			1,843
	Net periodic benefit cost	$	489		$	401		$	1,468		$	1,202
	Postretirement Benefit Plan
	Service cost	$	5		$	—		$	14		$	—
	Interest cost	36			37			108			110
	Amortization of prior service cost (credit)	27			(75		)	233			(225		)
	Amortization of unrecognized net gain	(18		)	(7		)	(55		)	(21		)
	Net periodic benefit cost (income)	$	50		$	(45	)	$	300		$	(136	)

Significant_Accounting_Policie2

Significant Accounting Policies (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Apr. 20, 2009	Jan. 31, 2008
	Pools
	Bank
Accounting Policies [Abstract]	'	'	'	'	'
Number of banks through which company operates	1	'	'	'	'
Number of regional banking units Chemical Bank operates through	4	'	'	'	'
Number of minimum days when principal or interest is past due is placed in nonaccrual category	'90 days	'	'	'	'
Number of minimum days in real estate residential loan when principal or interest is past due is placed in nonaccrual category	'120 days	'	'	'	'
Time period in which payments receive consistently and loans are returned to accrual status	'6 months	'	'	'	'
Number of pools of aggregate acquired loans based upon common risk characteristics	14	'	'	'	'
Time period sustained for payment history of principal and interest payments to move them to performing status	'6 months	'	'	'	'
Time period of real estate residential troubled debt restructurings reducing borrower's monthly payments by decreasing the interest rate charged on the loan	'24 months	'	'	'	'
Minimum number of days past due as to interest or principal payments in accruing loans moves to nonperforming loans	'90 days	'	'	'	'
Minimum amount of loan reviewed for detailed credit quality	$250,000	'	'	'	'
Revised time period for historical loan loss experience	'5 years	'	'	'	'
Minimum percentage of tax benefit is recognized for the amount likely to be realized	50.00%	'	'	'	'
Reserve for contingent income tax liabilities recorded	$0	$0	$0	'	'
Number of shares authorized to be repurchased	'	'	'	'	500,000
Stock repurchased (shares)	0	'	'	'	'
Number of remaining shares authorized to be repurchased (shares)	500,000	'	'	'	'
Preferred stock, shares authorized	200,000	200,000	200,000	200,000	'
Preferred stock, shares issued	0	0	0	'	'
Preferred stock, shares outstanding	0	'	'	'	'

Acquisitions_Activity_for_Acqu

Acquisitions (Activity for Acquired Loans) (Details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012
Activity for accretable yield includes contractually due interest of acquired loans	'		'
Balance at beginning of period	$49,390		$68,305
Additions (reductions)	-997	[1]	6,237	[1]
Accretion recognized in interest income	-13,235		-18,543
Reclassification from nonaccretable difference	125		0
Balance at end of period	$35,283		$55,999
[1]	Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.

Acquisitions_Textual_Details

Acquisitions (Textual) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 07, 2012	Dec. 07, 2012	Apr. 30, 2010	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 07, 2012
				Independent Bank [Member]	Independent Bank [Member]	OAK [Member]	OAK [Member]	OAK [Member]	OAK [Member]	Branch Offices [Member]
				Branches	Core Deposits [Member]	Offices				Independent Bank [Member]
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'	'	'
Number of branches acquired (branches)	'	'	'	21	'	'	'	'	'	'
Deposits acquired	'	'	'	$404,000,000	'	'	'	'	'	'
Loans acquired	'	'	'	44,000,000	'	627,000,000	'	'	'	'
Acquisition purchase price	'	'	'	'	'	83,700,000	'	'	'	8,100,000
Premium paid on deposits purchased	'	'	'	11,500,000	'	'	'	'	'	'
Premium paid as a percentage of deposits purchased (percent)	'	'	'	2.85%	'	'	'	'	'	'
Discount on loans purchased (percent)	'	'	'	1.75%	'	'	'	'	'	'
Goodwill	120,164,000	120,164,000	113,414,000	6,800,000	'	'	'	'	'	'
Intangibles acquired	'	'	'	'	5,600,000	'	'	'	'	'
Service provided by acquiree bank through number of branches	'	'	'	'	'	14	'	'	'	'
Assets of acquiree company	'	'	'	'	'	820,000,000	'	'	'	'
Deposits of acquiree company	'	'	'	'	'	693,000,000	'	'	'	'
Brokered deposits of acquiree company	'	'	'	'	'	193,000,000	'	'	'	'
Contractually required principal and interest payments of loan portfolio	'	'	'	'	'	683,000,000	'	'	'	'
Contractually required interest payments of loan portfolio	'	'	'	'	'	97,000,000	'	'	'	'
Expected principal cash flows of contractually required acquired loan portfolio	'	'	'	'	'	636,000,000	'	'	'	'
Expected interest cash flows of contractually required acquired loan portfolio	'	'	'	'	'	88,000,000	'	'	'	'
Expected interest cash flows of contractually required loan portfolio fair value	'	'	'	'	'	627,000,000	'	'	'	'
Nonaccretable difference	'	'	'	'	'	56,000,000	'	'	'	'
Expected credit losses	'	'	'	'	'	47,000,000	'	'	'	'
Certain Loans Acquired in Transfer, Accretable Yield	'	'	'	'	'	97,000,000	'	'	'	'
Outstanding contractual principal balance of acquired loan portfolio	'	'	'	'	'	'	334,000,000	419,000,000	440,000,000	'
Carrying amount of acquired loan portfolio	'	'	'	'	'	'	$309,000,000	$393,000,000	$413,000,000	'

Investment_Securities_Summary_

Investment Securities (Summary of Amortized Cost and Fair Value of Available-For-Sale Investment Securities) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	$707,655	$580,234	$639,315
Investment securities available-for-sale, Unrealized Gains	3,784	7,518	8,448
Investment securities available-for-sale, Unrealized Losses	6,293	943	1,185
Available-for-sale Securities, Total	705,146	586,809	646,578
Government sponsored agencies [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	86,065	97,529	101,576
Investment securities available-for-sale, Unrealized Gains	264	241	182
Investment securities available-for-sale, Unrealized Losses	404	213	266
Available-for-sale Securities, Total	85,925	97,557	101,492
State and political subdivisions [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	44,191	47,663	49,707
Investment securities available-for-sale, Unrealized Gains	1,386	2,302	2,538
Investment securities available-for-sale, Unrealized Losses	5	0	7
Available-for-sale Securities, Total	45,572	49,965	52,238
Residential mortgage-backed securities [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	310,550	96,320	101,709
Investment securities available-for-sale, Unrealized Gains	1,144	3,100	3,543
Investment securities available-for-sale, Unrealized Losses	3,534	9	16
Available-for-sale Securities, Total	308,160	99,411	105,236
Collateralized Mortgage Obligations [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	200,407	262,790	297,960
Investment securities available-for-sale, Unrealized Gains	199	984	1,392
Investment securities available-for-sale, Unrealized Losses	2,148	182	274
Available-for-sale Securities, Total	198,458	263,592	299,078
Corporate bonds [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	65,053	69,788	82,219
Investment securities available-for-sale, Unrealized Gains	583	546	509
Investment securities available-for-sale, Unrealized Losses	202	539	622
Available-for-sale Securities, Total	65,434	69,795	82,106
Preferred stock [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	1,389	6,144	6,144
Investment securities available-for-sale, Unrealized Gains	208	345	284
Investment securities available-for-sale, Unrealized Losses	0	0	0
Available-for-sale Securities, Total	$1,597	$6,489	$6,428

Investment_Securities_Summary_1

Investment Securities (Summary of Amortized Cost and Fair Value of Held-To-Maturity Investment Securities) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Held-to-maturity Securities	'	'	'
Investment securities held-to-maturity, Amortized Cost	$282,579	$229,977	$221,536
Investment securities held-to-maturity, Unrealized Gains	5,978	8,087	8,661
Investment securities held-to-maturity, Unrealized Losses	12,691	8,142	7,012
Total Held-to-maturity securities, Debt maturities, Fair Value	275,866	229,922	223,185
State and political subdivisions [Member]	'	'	'
Held-to-maturity Securities	'	'	'
Investment securities held-to-maturity, Amortized Cost	272,079	219,477	211,036
Investment securities held-to-maturity, Unrealized Gains	5,978	8,087	8,661
Investment securities held-to-maturity, Unrealized Losses	8,441	3,367	1,712
Total Held-to-maturity securities, Debt maturities, Fair Value	269,616	224,197	217,985
Trust Preferred Securities [Member]	'	'	'
Held-to-maturity Securities	'	'	'
Investment securities held-to-maturity, Amortized Cost	10,500	10,500	10,500
Investment securities held-to-maturity, Unrealized Gains	0	0	0
Investment securities held-to-maturity, Unrealized Losses	4,250	4,775	5,300
Total Held-to-maturity securities, Debt maturities, Fair Value	$6,250	$5,725	$5,200

Investment_Securities_Maturiti

Investment Securities (Maturities of Debt Securities) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Investment Securities Available-for-Sale:	'	'	'
Due in one year or less, Amortized Cost	$91,500	'	'
Due after one year through five years, Amortized Cost	117,337	'	'
Due after five years through ten years, Amortized Cost	426,031	'	'
Due after ten years, Amortized Cost	71,398	'	'
Preferred stock, Amortized Cost	1,389	'	'
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	707,655	'	'
Due in one year or less , Fair Value	91,946	'	'
Due after one year through five years, Fair Value	118,555	'	'
Due after five years through ten years, Fair Value	422,118	'	'
Due after ten years, Fair Value	70,930	'	'
Preferred stock, Fair Value	1,597	'	'
Total Available-for-sale securities, Debt maturities, Fair Value	705,146	'	'
Investment Securities Held-to-Maturity:	'	'	'
Due in one year or less, Amortized Cost	42,112	'	'
Due after one year through five years, Amortized Cost	114,020	'	'
Due after five years through ten years, Amortized Cost	74,316	'	'
Due after ten years, Amortized Cost	52,131	'	'
Total Held-to-maturity securities, Debt maturities, Amortized Cost	282,579	229,977	221,536
Due in one year or less , Fair Value	42,179	'	'
Due after one year through five years, Fair Value	115,646	'	'
Due after five years through ten years, Fair Value	74,353	'	'
Due after ten years, Fair Value	43,688	'	'
Total Held-to-maturity securities, Debt maturities, Fair Value	$275,866	$229,922	$223,185

Investment_Securities_Summary_2

Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	$570,518	$141,129	$141,107
Less Than 12 Months, Gross Unrealized Losses	12,375	2,734	2,536
12 Months or More, Fair Value	86,785	86,618	107,211
12 Months or More, Gross Unrealized Losses	6,609	6,351	5,661
Total, Fair Value	657,303	227,747	248,318
Total, Gross Unrealized Losses	18,984	9,085	8,197
Government sponsored agencies [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	43,816	46,103	39,729
Less Than 12 Months, Gross Unrealized Losses	223	213	248
12 Months or More, Fair Value	14,395	0	8,808
12 Months or More, Gross Unrealized Losses	181	0	18
Total, Fair Value	58,211	46,103	48,537
Total, Gross Unrealized Losses	404	213	266
State and political subdivisions [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	120,232	70,675	69,841
Less Than 12 Months, Gross Unrealized Losses	6,918	2,257	1,711
12 Months or More, Fair Value	30,915	8,046	1,533
12 Months or More, Gross Unrealized Losses	1,528	1,110	8
Total, Fair Value	151,147	78,721	71,374
Total, Gross Unrealized Losses	8,446	3,367	1,719
Residential mortgage-backed securities [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	267,495	273	32
Less Than 12 Months, Gross Unrealized Losses	3,532	1	1
12 Months or More, Fair Value	40	1,305	19,704
12 Months or More, Gross Unrealized Losses	2	8	15
Total, Fair Value	267,535	1,578	19,736
Total, Gross Unrealized Losses	3,534	9	16
Collateralized Mortgage Obligations [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	129,049	19,331	12,036
Less Than 12 Months, Gross Unrealized Losses	1,617	10	45
12 Months or More, Fair Value	15,302	36,835	47,066
12 Months or More, Gross Unrealized Losses	531	172	229
Total, Fair Value	144,351	56,166	59,102
Total, Gross Unrealized Losses	2,148	182	274
Corporate bonds [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	9,926	4,747	19,469
Less Than 12 Months, Gross Unrealized Losses	85	253	531
12 Months or More, Fair Value	19,883	34,707	24,900
12 Months or More, Gross Unrealized Losses	117	286	91
Total, Fair Value	29,809	39,454	44,369
Total, Gross Unrealized Losses	202	539	622
Trust Preferred Securities [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	0	0	0
Less Than 12 Months, Gross Unrealized Losses	0	0	0
12 Months or More, Fair Value	6,250	5,725	5,200
12 Months or More, Gross Unrealized Losses	4,250	4,775	5,300
Total, Fair Value	6,250	5,725	5,200
Total, Gross Unrealized Losses	$4,250	$4,775	$5,300

Investment_Securities_Textual_

Investment Securities (Textual) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Investments, Debt and Equity Securities [Abstract]	'
preferred stock investment security carried on a cost basis	$4.80
gain on sale of preferred stock investment security	0.2
Trust preferred investment securities held to maturity	10.5
Trust preferred investment security of Non Public bank company	10
Interest in Trust preferred investment security	100.00%
Remaining trust preferred investment security of Non Public bank company	0.5
Interest in another trust preferred investment security	10.00%
Carrying value of trust preferred investment security one	10
Carrying value of trust preferred investment security two	0.5
Fair value of trust preferred investment security one	6
Fair value of trust preferred investment security two	0.2
Unrealized loss on trust preferred investment securities	4.3
Combined unrealized loss	4.3
Unrealized loss on trust preferred securities.	$4.30

Loans_Summary_of_Loans_Details

Loans (Summary of Loans) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Summary of loans under portfolio	'	'	'
Commercial loan	$2,445,787	$2,264,820	$2,159,893
Consumer loan	2,076,884	1,902,915	1,859,266
Total loans	4,522,671	4,167,735	4,019,159
Commercial [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Commercial loan	1,128,122	1,002,722	951,938
Real estate commercial [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Commercial loan	1,215,631	1,161,861	1,117,073
Real estate construction [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Commercial loan	78,361	62,689	56,071
Land development [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Commercial loan	23,673	37,548	34,811
Real estate residential [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Consumer loan	942,777	883,835	880,295
Consumer installment [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Consumer loan	622,040	546,036	538,412
Home equity [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Consumer loan	$512,067	$473,044	$440,559

Loans_Summary_of_Recorded_Inve

Loans (Summary of Recorded Investment of Commercial Loans by Risk Rating Categories) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	$2,445,787	$2,264,820	$2,159,893
Commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,128,122	1,002,722	951,938
Real estate commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,215,631	1,161,861	1,117,073
Real estate construction [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	78,361	62,689	56,071
Land development [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	23,673	37,548	34,811
Originated Portfolio [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,183,788	1,927,956	1,805,862
Originated Portfolio [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,010,267	1,736,870	1,615,486
Originated Portfolio [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	55,132	83,883	73,809
Originated Portfolio [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	74,820	49,541	53,375
Originated Portfolio [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	41,076	51,286	59,823
Originated Portfolio [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,493	6,376	3,369
Originated Portfolio [Member] | Commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,040,795	896,610	838,682
Originated Portfolio [Member] | Commercial [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	974,903	827,112	772,555
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	16,439	38,066	33,819
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	37,644	16,831	17,091
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	9,753	12,540	14,790
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,056	2,061	427
Originated Portfolio [Member] | Real estate commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,060,558	956,165	904,399
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	963,394	846,901	793,237
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	37,572	45,261	38,880
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	30,969	26,343	30,971
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	28,186	33,345	38,369
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	437	4,315	2,942
Originated Portfolio [Member] | Real estate construction [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	65,788	49,123	38,297
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	64,210	47,847	37,346
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	58	59	18
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,337	0	0
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	183	1,217	933
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Originated Portfolio [Member] | Land development [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	16,647	26,058	24,484
Originated Portfolio [Member] | Land development [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	7,760	15,010	12,348
Originated Portfolio [Member] | Land development [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,063	497	1,092
Originated Portfolio [Member] | Land development [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	4,870	6,367	5,313
Originated Portfolio [Member] | Land development [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,954	4,184	5,731
Originated Portfolio [Member] | Land development [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	261,999	336,864	354,031
Acquired Portfolio [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	241,059	303,765	315,541
Acquired Portfolio [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	7,457	14,362	17,905
Acquired Portfolio [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	8,839	11,846	13,779
Acquired Portfolio [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	4,644	6,891	6,806
Acquired Portfolio [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	87,327	106,112	113,256
Acquired Portfolio [Member] | Commercial [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	82,648	93,281	97,308
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,620	8,225	10,899
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	992	2,169	2,107
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,067	2,437	2,942
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	155,073	205,696	212,674
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	141,234	188,499	192,903
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	4,837	5,900	7,006
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	7,847	9,677	11,672
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,155	1,620	1,093
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	12,573	13,566	17,774
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	12,573	13,566	17,774
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Land development [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	7,026	11,490	10,327
Acquired Portfolio [Member] | Land development [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	4,604	8,419	7,556
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	237	0
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,422	2,834	2,771
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	$0	$0	$0

Loans_Summary_of_Recorded_Inve1

Loans (Summary of Recorded Investment of Consumer Loans by Risk Rating Categories) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	$2,076,884	$1,902,915	$1,859,266
Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	942,777	883,835	880,295
Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	622,040	546,036	538,412
Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	512,067	473,044	440,559
Originated Loans [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	2,029,940	1,847,184	1,800,685
Originated Loans [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	930,781	869,870	865,025
Originated Loans [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	620,011	544,078	536,239
Originated Loans [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	479,148	433,236	399,421
Originated Loans [Member] | Performing [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	2,013,716	1,827,955	1,780,073
Originated Loans [Member] | Performing [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	918,931	854,882	849,385
Originated Loans [Member] | Performing [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	619,346	543,339	535,277
Originated Loans [Member] | Performing [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	475,439	429,734	395,411
Originated Loans [Member] | Nonperforming [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	16,224	19,229	20,612
Originated Loans [Member] | Nonperforming [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	11,850	14,988	15,640
Originated Loans [Member] | Nonperforming [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	665	739	962
Originated Loans [Member] | Nonperforming [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	3,709	3,502	4,010
Acquired Loans [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	46,944	55,731	58,581
Acquired Loans [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	11,996	13,965	15,270
Acquired Loans [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	2,029	1,958	2,173
Acquired Loans [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	32,919	39,808	41,138
Acquired Loans [Member] | Performing [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	46,684	55,438	57,975
Acquired Loans [Member] | Performing [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	11,918	13,843	14,928
Acquired Loans [Member] | Performing [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	2,029	1,958	2,173
Acquired Loans [Member] | Performing [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	32,737	39,637	40,874
Acquired Loans [Member] | Nonperforming [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	260	293	606
Acquired Loans [Member] | Nonperforming [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	78	122	342
Acquired Loans [Member] | Nonperforming [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	0	0	0
Acquired Loans [Member] | Nonperforming [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	$182	$171	$264

Loans_Summary_of_Nonperforming

Loans (Summary of Nonperforming Loans) (Details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Summary of nonperforming loans	'	'	'
Total nonperforming TDRs	$52,944	$48,566	$40,861
Total loans	4,522,671	4,167,735	4,019,159
Number of minimum days for performing and nonperforming trouble debt restructuring	'90 days	'	'
Commercial Loan Portfolio [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonperforming TDRs	35,213	29,665	21,303
Total loans	2,445,787	2,264,820	2,159,893
Consumer Loan Portfolio [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonperforming TDRs	17,731	18,901	19,558
Total loans	2,076,884	1,902,915	1,859,266
Nonperforming [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	55,286	71,298	78,324
Total accruing loans contractually past due 90 days or more as to interest or principal payments	1,659	2,359	2,098
Total nonperforming TDRs	18,873	17,197	10,455
Total loans	75,818	90,854	90,877
Nonperforming [Member] | Commercial Loan Portfolio [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonperforming TDRs	15,744	13,876	6,553
Nonperforming [Member] | Consumer Loan Portfolio [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonperforming TDRs	3,129	3,321	3,902
Nonperforming [Member] | Commercial [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	11,809	14,601	15,217
Total accruing loans contractually past due 90 days or more as to interest or principal payments	281	0	273
Nonperforming [Member] | Real estate commercial [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	28,623	37,660	41,311
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	87	247
Nonperforming [Member] | Real Estate Construction Loans [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	183	1,217	933
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0	0
Nonperforming [Member] | Land Development Loans [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	2,954	4,184	5,731
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0	0
Nonperforming [Member] | Real estate residential [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	8,029	10,164	11,307
Total accruing loans contractually past due 90 days or more as to interest or principal payments	692	1,503	431
Nonperforming [Member] | Consumer Installment Loans [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	665	739	876
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0	0
Nonperforming [Member] | Home Equity Loans [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	3,023	2,733	2,949
Total accruing loans contractually past due 90 days or more as to interest or principal payments	$686	$769	$1,147

Loans_Summary_of_Impaired_Loan

Loans (Summary of Impaired Loans by Classes of Loans) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	$30,174	$42,961	$45,322
Unpaid Principal Balance	32,341	43,751	48,835
Related Valuation Allowance	4,223	8,108	8,659
Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	85,666	86,002	83,254
Unpaid Principal Balance	108,095	106,354	103,145
Related Valuation Allowance	0	0	0
Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	115,840	128,963	128,576
Unpaid Principal Balance	140,436	150,105	151,980
Related Valuation Allowance	4,223	8,108	8,659
Commercial [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	5,059	6,368	6,743
Unpaid Principal Balance	5,803	6,818	7,357
Related Valuation Allowance	1,857	1,966	2,240
Commercial [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	21,543	23,230	19,768
Unpaid Principal Balance	25,642	27,959	24,517
Related Valuation Allowance	0	0	0
Commercial [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	26,602	29,598	26,511
Unpaid Principal Balance	31,445	34,777	31,874
Related Valuation Allowance	1,857	1,966	2,240
Real estate commercial [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	6,684	17,267	19,694
Unpaid Principal Balance	7,901	17,607	22,593
Related Valuation Allowance	1,651	5,359	5,344
Real estate commercial [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	43,178	37,223	36,225
Unpaid Principal Balance	57,256	48,531	48,187
Related Valuation Allowance	0	0	0
Real estate commercial [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	49,862	54,490	55,919
Unpaid Principal Balance	65,157	66,138	70,780
Related Valuation Allowance	1,651	5,359	5,344
Real estate construction [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	183	171	127
Unpaid Principal Balance	253	171	127
Related Valuation Allowance	33	75	43
Real estate construction [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	133	1,046	806
Unpaid Principal Balance	133	1,116	806
Related Valuation Allowance	0	0	0
Real estate construction [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	316	1,217	933
Unpaid Principal Balance	386	1,287	933
Related Valuation Allowance	33	75	43
Land development [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	517	254	2,800
Unpaid Principal Balance	653	254	2,800
Related Valuation Allowance	97	50	383
Land development [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	9,095	10,867	7,723
Unpaid Principal Balance	13,347	15,112	10,903
Related Valuation Allowance	0	0	0
Land development [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	9,612	11,121	10,523
Unpaid Principal Balance	14,000	15,366	13,703
Related Valuation Allowance	97	50	383
Real estate residential [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	17,731	18,901	15,958
Unpaid Principal Balance	17,731	18,901	15,958
Related Valuation Allowance	585	658	649
Real estate residential [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	8,029	10,164	14,907
Unpaid Principal Balance	8,029	10,164	14,907
Related Valuation Allowance	0	0	0
Real estate residential [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	25,760	29,065	30,865
Unpaid Principal Balance	25,760	29,065	30,865
Related Valuation Allowance	585	658	649
Consumer installment [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	665	739	876
Unpaid Principal Balance	665	739	876
Related Valuation Allowance	0	0	0
Consumer installment [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	665	739	876
Unpaid Principal Balance	665	739	876
Related Valuation Allowance	0	0	0
Home equity [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	3,023	2,733	2,949
Unpaid Principal Balance	3,023	2,733	2,949
Related Valuation Allowance	0	0	0
Home equity [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	3,023	2,733	2,949
Unpaid Principal Balance	3,023	2,733	2,949
Related Valuation Allowance	$0	$0	$0

Loans_Summary_of_Information_R

Loans (Summary of Information Related to Impaired Loans) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	$116,869	$132,202	$122,100	$138,079
Interest income recognized related to loans with impaired status	858	720	2,732	2,491
Commercial [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	27,025	28,683	26,894	27,684
Interest income recognized related to loans with impaired status	215	149	633	602
Real estate commercial [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	50,266	54,524	53,482	59,063
Interest income recognized related to loans with impaired status	284	212	984	642
Real estate construction [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	414	912	395	470
Interest income recognized related to loans with impaired status	2	0	7	0
Land development [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	9,615	10,582	10,470	8,869
Interest income recognized related to loans with impaired status	79	71	261	216
Real estate residential [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	25,826	33,652	27,216	37,861
Interest income recognized related to loans with impaired status	278	288	847	1,031
Consumer installment [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	632	909	666	1,222
Interest income recognized related to loans with impaired status	0	0	0	0
Home equity [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	3,091	2,940	2,977	2,910
Interest income recognized related to loans with impaired status	$0	$0	$0	$0

Loans_Summary_of_the_Aging_Sta

Loans (Summary of the Aging Status of the Recorded Investment in Loans by Portfolio Segment/Class) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Originated Portfolio [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	$21,706	$17,045	$22,734
Financing receivable, recorded investment 61 to 89 days past due	10,061	3,679	4,331
Financing receivable, recorded investment accruing loans past due 90 days or more	1,659	2,359	2,098
Financing receivable, recorded investment, Nonaccrual loans	55,286	71,298	78,324
Financing receivable recorded investment, Total past due	88,712	94,381	107,487
Financing receivable, recorded investment, current	4,125,016	3,680,759	3,499,060
Financing receivable, recorded investment, Total loans	4,213,728	3,775,140	3,606,547
Originated Portfolio [Member] | Commercial [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	7,833	3,999	9,707
Financing receivable, recorded investment 61 to 89 days past due	1,542	730	1,374
Financing receivable, recorded investment accruing loans past due 90 days or more	281	0	273
Financing receivable, recorded investment, Nonaccrual loans	11,809	14,601	15,217
Financing receivable recorded investment, Total past due	21,465	19,330	26,571
Financing receivable, recorded investment, current	1,019,330	877,280	812,111
Financing receivable, recorded investment, Total loans	1,040,795	896,610	838,682
Originated Portfolio [Member] | Real estate commercial [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	6,533	5,852	4,929
Financing receivable, recorded investment 61 to 89 days past due	2,274	2,089	1,660
Financing receivable, recorded investment accruing loans past due 90 days or more	0	87	247
Financing receivable, recorded investment, Nonaccrual loans	28,623	37,660	41,311
Financing receivable recorded investment, Total past due	37,430	45,688	48,147
Financing receivable, recorded investment, current	1,023,128	910,477	856,252
Financing receivable, recorded investment, Total loans	1,060,558	956,165	904,399
Originated Portfolio [Member] | Real estate construction [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	90	0	0
Financing receivable, recorded investment 61 to 89 days past due	5,385	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	183	1,217	933
Financing receivable recorded investment, Total past due	5,658	1,217	933
Financing receivable, recorded investment, current	60,130	47,906	37,364
Financing receivable, recorded investment, Total loans	65,788	49,123	38,297
Originated Portfolio [Member] | Land development [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	187	0	48
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	2,954	4,184	5,731
Financing receivable recorded investment, Total past due	3,141	4,184	5,779
Financing receivable, recorded investment, current	13,506	21,874	18,705
Financing receivable, recorded investment, Total loans	16,647	26,058	24,484
Originated Portfolio [Member] | Real estate residential [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	1,739	3,161	3,208
Financing receivable, recorded investment 61 to 89 days past due	76	55	97
Financing receivable, recorded investment accruing loans past due 90 days or more	692	1,503	431
Financing receivable, recorded investment, Nonaccrual loans	8,029	10,164	11,307
Financing receivable recorded investment, Total past due	10,536	14,883	15,043
Financing receivable, recorded investment, current	920,245	854,987	849,982
Financing receivable, recorded investment, Total loans	930,781	869,870	865,025
Originated Portfolio [Member] | Consumer installment [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	2,980	2,415	3,299
Financing receivable, recorded investment 61 to 89 days past due	350	378	470
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	665	739	876
Financing receivable recorded investment, Total past due	3,995	3,532	4,645
Financing receivable, recorded investment, current	616,016	540,546	531,594
Financing receivable, recorded investment, Total loans	620,011	544,078	536,239
Originated Portfolio [Member] | Home equity [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	2,344	1,618	1,543
Financing receivable, recorded investment 61 to 89 days past due	434	427	730
Financing receivable, recorded investment accruing loans past due 90 days or more	686	769	1,147
Financing receivable, recorded investment, Nonaccrual loans	3,023	2,733	2,949
Financing receivable recorded investment, Total past due	6,487	5,547	6,369
Financing receivable, recorded investment, current	472,661	427,689	393,052
Financing receivable, recorded investment, Total loans	479,148	433,236	399,421
Acquired Portfolio [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	1,162	625	1,498
Financing receivable, recorded investment 61 to 89 days past due	80	15	54
Financing receivable, recorded investment accruing loans past due 90 days or more	7,610	9,099	9,391
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	8,852	9,739	10,943
Financing receivable, recorded investment, current	300,091	382,856	401,669
Financing receivable, recorded investment, Total loans	308,943	392,595	412,612
Acquired Portfolio [Member] | Commercial [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	67	0	0
Financing receivable, recorded investment 61 to 89 days past due	0	0	15
Financing receivable, recorded investment accruing loans past due 90 days or more	1,574	2,834	3,356
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	1,641	2,834	3,371
Financing receivable, recorded investment, current	85,686	103,278	109,885
Financing receivable, recorded investment, Total loans	87,327	106,112	113,256
Acquired Portfolio [Member] | Real estate commercial [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	439	287	1,262
Financing receivable, recorded investment 61 to 89 days past due	0	15	0
Financing receivable, recorded investment accruing loans past due 90 days or more	3,355	3,139	2,390
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	3,794	3,441	3,652
Financing receivable, recorded investment, current	151,279	202,255	209,022
Financing receivable, recorded investment, Total loans	155,073	205,696	212,674
Acquired Portfolio [Member] | Real estate construction [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	0	0	0
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	0	0	0
Financing receivable, recorded investment, current	12,573	13,566	17,774
Financing receivable, recorded investment, Total loans	12,573	13,566	17,774
Acquired Portfolio [Member] | Land development [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	0	0	0
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	2,422	2,834	3,038
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	2,422	2,834	3,038
Financing receivable, recorded investment, current	4,604	8,656	7,289
Financing receivable, recorded investment, Total loans	7,026	11,490	10,327
Acquired Portfolio [Member] | Real estate residential [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	264	123	80
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	77	122	343
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	341	245	423
Financing receivable, recorded investment, current	11,655	13,720	14,847
Financing receivable, recorded investment, Total loans	11,996	13,965	15,270
Acquired Portfolio [Member] | Consumer installment [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	3	10	18
Financing receivable, recorded investment 61 to 89 days past due	1	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	4	10	18
Financing receivable, recorded investment, current	2,025	1,948	2,155
Financing receivable, recorded investment, Total loans	2,029	1,958	2,173
Acquired Portfolio [Member] | Home equity [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	389	205	138
Financing receivable, recorded investment 61 to 89 days past due	79	0	39
Financing receivable, recorded investment accruing loans past due 90 days or more	182	170	264
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	650	375	441
Financing receivable, recorded investment, current	32,269	39,433	40,697
Financing receivable, recorded investment, Total loans	$32,919	$39,808	$41,138

Loans_Summary_of_TDRs_Details

Loans (Summary of TDRs) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Schedule of corporation's TDRs	'	'	'
Total nonperforming TDRs	$52,944	$48,566	$40,861
Commercial Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total nonperforming TDRs	35,213	29,665	21,303
Consumer Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total nonperforming TDRs	17,731	18,901	19,558
Performing [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total nonperforming TDRs	34,071	31,369	30,406
Performing [Member] | Commercial Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total nonperforming TDRs	19,469	15,789	14,750
Performing [Member] | Consumer Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total nonperforming TDRs	14,602	15,580	15,656
Nonperforming [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total nonperforming TDRs	18,873	17,197	10,455
Nonperforming [Member] | Commercial Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total nonperforming TDRs	15,744	13,876	6,553
Nonperforming [Member] | Consumer Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total nonperforming TDRs	$3,129	$3,321	$3,902

Loans_Summary_of_Performing_an

Loans (Summary of Performing and Nonperforming TDRs Modified During the Period) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
	Loans	Loans	Loans	Loans
Schedule providing information on performing and nonperforming TDRs	'	'	'	'
Performing and nonperforming modified TDRs, Number of loans	'	'	78	104
Performing and nonperforming modified TDRs, Pre-modification recorded investment	'	'	$16,242	$17,876
Performing and nonperforming modified TDRs, Post-modification recorded investment	'	'	16,143	17,665
Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on performing and nonperforming TDRs	'	'	'	'
Performing and nonperforming modified TDRs, Number of loans	24	32	'	'
Performing and nonperforming modified TDRs, Pre-modification recorded investment	4,099	3,443	'	'
Performing and nonperforming modified TDRs, Post-modification recorded investment	4,056	3,392	'	'
Subtotal-commercial loan portfolio [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on performing and nonperforming TDRs	'	'	'	'
Performing and nonperforming modified TDRs, Number of loans	5	17	30	39
Performing and nonperforming modified TDRs, Pre-modification recorded investment	2,452	2,091	12,708	10,793
Performing and nonperforming modified TDRs, Post-modification recorded investment	2,452	2,091	12,708	10,793
Consumer loan portfolio (real estate residential) [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on performing and nonperforming TDRs	'	'	'	'
Performing and nonperforming modified TDRs, Number of loans	19	15	'	'
Performing and nonperforming modified TDRs, Pre-modification recorded investment	1,647	1,352	'	'
Performing and nonperforming modified TDRs, Post-modification recorded investment	1,604	1,301	'	'
Consumer loan portfolio (real estate residential) [Member] | Consumer Portfolio Segment [Member]	'	'	'	'
Schedule providing information on performing and nonperforming TDRs	'	'	'	'
Performing and nonperforming modified TDRs, Number of loans	'	'	48	65
Performing and nonperforming modified TDRs, Pre-modification recorded investment	'	'	3,534	7,083
Performing and nonperforming modified TDRs, Post-modification recorded investment	'	'	3,435	6,872
Commercial [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on performing and nonperforming TDRs	'	'	'	'
Performing and nonperforming modified TDRs, Number of loans	2	9	11	19
Performing and nonperforming modified TDRs, Pre-modification recorded investment	352	665	3,370	3,891
Performing and nonperforming modified TDRs, Post-modification recorded investment	352	665	3,370	3,891
Real estate commercial [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on performing and nonperforming TDRs	'	'	'	'
Performing and nonperforming modified TDRs, Number of loans	3	8	16	19
Performing and nonperforming modified TDRs, Pre-modification recorded investment	2,100	1,426	8,701	5,264
Performing and nonperforming modified TDRs, Post-modification recorded investment	2,100	1,426	8,701	5,264
Land development [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on performing and nonperforming TDRs	'	'	'	'
Performing and nonperforming modified TDRs, Number of loans	0	0	3	1
Performing and nonperforming modified TDRs, Pre-modification recorded investment	0	0	637	1,638
Performing and nonperforming modified TDRs, Post-modification recorded investment	$0	$0	$637	$1,638

Loans_Summary_of_TDRs_with_a_P

Loans (Summary of TDRs with a Payment Default During the Period) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
	Loans	Loans	Loans	Loans
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	'	'	13	13
Financing receivable modification subsequent default recorded investment	'	'	$4,493	$5,719
Commercial Loan Portfolio [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	9	6	'	'
Financing receivable modification subsequent default recorded investment	3,690	4,439	'	'
Commercial [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	1	2	2	3
Financing receivable modification subsequent default recorded investment	748	1,240	1,182	1,300
Real estate commercial [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	4	3	4	5
Financing receivable modification subsequent default recorded investment	2,833	2,457	2,833	3,293
Subtotal-commercial loan portfolio [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	5	5	6	8
Financing receivable modification subsequent default recorded investment	3,581	3,697	4,015	4,593
Consumer loan portfolio (real estate residential) [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	4	1	'	'
Financing receivable modification subsequent default recorded investment	109	742	'	'
Consumer loan portfolio (real estate residential) [Member] | Consumer Portfolio Segment [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	'	'	7	5
Financing receivable modification subsequent default recorded investment	'	'	$478	$1,126

Loans_Schedule_of_the_Allowanc

Loans (Schedule of the Allowance for Loan Losses) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'	'	'	'	'
Beginning balance	$82,184	$86,711	$84,491	$88,333	'
Provision for loan losses	3,000	4,500	9,000	13,500	'
Charge-offs	-4,430	-7,596	-15,265	-20,315	'
Recoveries	778	1,079	3,306	3,176	'
Ending balance	81,532	84,694	81,532	84,694	'
Allowance for loan losses	'	'	'	'	'
Loans individually evaluated for impairment related to allowance for loan losses	4,223	8,659	4,223	8,659	8,108
Loans collectively evaluated for impairment related to allowance for loan losses	76,809	75,535	76,809	75,535	75,883
Loans acquired with deteriorated credit quality related to allowance for loan losses	500	500	500	500	500
Total	81,532	84,694	81,532	84,694	'
Loans individually evaluated for impairment related to recorded investment (loan balance)	96,513	104,053	96,513	104,053	106,228
Loans collectively evaluated for impairment related to recorded investment (loan balance)	4,117,215	3,502,494	4,117,215	3,502,494	3,668,912
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	308,943	412,612	308,943	412,612	392,595
Total loans	4,522,671	4,019,159	4,522,671	4,019,159	4,167,735
Commercial Loan Portfolio [Member]	'	'	'	'	'
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'	'	'	'	'
Beginning balance	47,780	53,759	49,975	55,645	'
Provision for loan losses	2,810	2,365	5,815	6,003	'
Charge-offs	-2,637	-4,754	-9,374	-11,330	'
Recoveries	374	460	1,911	1,512	'
Ending balance	48,327	51,830	48,327	51,830	'
Allowance for loan losses	'	'	'	'	'
Loans individually evaluated for impairment related to allowance for loan losses	3,638	8,010	3,638	8,010	7,450
Loans collectively evaluated for impairment related to allowance for loan losses	44,689	43,820	44,689	43,820	42,525
Loans acquired with deteriorated credit quality related to allowance for loan losses	0	0	0	0	0
Total	48,327	51,830	48,327	51,830	'
Loans individually evaluated for impairment related to recorded investment (loan balance)	78,782	84,495	78,782	84,495	87,327
Loans collectively evaluated for impairment related to recorded investment (loan balance)	2,105,006	1,721,367	2,105,006	1,721,367	1,840,629
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	261,999	354,031	261,999	354,031	336,864
Total loans	2,445,787	2,159,893	2,445,787	2,159,893	2,264,820
Consumer Loan Portfolio [Member]	'	'	'	'	'
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'	'	'	'	'
Beginning balance	28,745	29,784	29,333	29,166	'
Provision for loan losses	2,165	1,765	4,684	7,481	'
Charge-offs	-1,793	-2,842	-5,891	-8,985	'
Recoveries	404	619	1,395	1,664	'
Ending balance	29,521	29,326	29,521	29,326	'
Allowance for loan losses	'	'	'	'	'
Loans individually evaluated for impairment related to allowance for loan losses	585	649	585	649	658
Loans collectively evaluated for impairment related to allowance for loan losses	28,436	28,177	28,436	28,177	28,175
Loans acquired with deteriorated credit quality related to allowance for loan losses	500	500	500	500	500
Total	29,521	29,326	29,521	29,326	'
Loans individually evaluated for impairment related to recorded investment (loan balance)	17,731	19,558	17,731	19,558	18,901
Loans collectively evaluated for impairment related to recorded investment (loan balance)	2,012,209	1,781,127	2,012,209	1,781,127	1,828,283
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	46,944	58,581	46,944	58,581	55,731
Total loans	2,076,884	1,859,266	2,076,884	1,859,266	1,902,915
Unallocated [Member]	'	'	'	'	'
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'	'	'	'	'
Beginning balance	5,659	3,168	5,183	3,522	'
Provision for loan losses	-1,975	370	-1,499	16	'
Charge-offs	0	0	0	0	'
Recoveries	0	0	0	0	'
Ending balance	3,684	3,538	3,684	3,538	'
Allowance for loan losses	'	'	'	'	'
Loans individually evaluated for impairment related to allowance for loan losses	0	0	0	0	0
Loans collectively evaluated for impairment related to allowance for loan losses	3,684	3,538	3,684	3,538	5,183
Loans acquired with deteriorated credit quality related to allowance for loan losses	0	0	0	0	0
Total	3,684	3,538	3,684	3,538	'
Loans individually evaluated for impairment related to recorded investment (loan balance)	0	0	0	0	0
Loans collectively evaluated for impairment related to recorded investment (loan balance)	0	0	0	0	0
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	0	0	0	0	0
Total loans	$0	$0	$0	$0	$0

Loans_Textual_Details

Loans (Textual) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
	BaordOfDirectors
	Tenants
	Segment
	Loans
Loans (Textual) [Abstract]	'	'	'
Number of portfolio segment	2	'	'
Number of classes of loans	7	'	'
Number of tenants under lease of real estate	1	'	'
Number of members of the board of directors in loan committee	9	'	'
Minimum due period of loans consider in a nonperforming status	'90 days	'	'
Total nonaccrual loans	$39.10	$47.50	$37
Difference between recorded investment and unpaid principal balance of loan	24.6	21.1	23.4
Confirmed losses (partial charge-offs)	21.2	17.3	19.8
Fair value of discount adjustment	3.4	3.8	3.6
Acquired impaired loans	7.6	9.1	9.4
Performing trouble debt restructuring under impaired loans	34.1	31.4	30.4
Financing receivable allowance for acquired loans	0.5	0.5	0.5
Number of minimum days for performing and nonperforming trouble debt restructuring	'90 days	'	'
Commercial Loan Portfolio [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Minimum value of loan requires executive and senior officer approval	1.5	'	'
Consumer Portfolio Segment [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Original contractual terms	'90 days	'	'
Minimum due period of loans consider in a nonperforming status	'90 days	'	'
Commercial [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Minimum value of loan requires group loan authority approval	1	'	'
Maximum value of loan requires executive and senior officer approval	3.5	'	'
Real Estate Residential Loans [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Period for loan secured under real estate residential security	'15 years	'	'
Loan-to-value ratio at the time of origination	80.00%	'	'
Land Development Loans [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Maximum period for payment of loan	'12 months	'	'
Maximum [Member] | Commercial Loan Portfolio [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Maximum value of loan requires group loan authority approval	5	'	'
Other loans requiring director loan committee approval depending on risk rating and credit action required	5	'	'
Maximum [Member] | Real Estate Residential Loans [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Upper limit of number of family residential properties	4	'	'
Minimum [Member] | Commercial Loan Portfolio [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Minimum value of loan requires group loan authority approval	1	'	'
Maximum value of loans depending on risk rating and requires credit action from board of directors	10	'	'
Minimum [Member] | Commercial [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Minimum value of loans requiring only director loan committee approval	$5	'	'
Minimum [Member] | Real Estate Residential Loans [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Lower limit of number of family residential properties	1	'	'

Intangible_Assets_Net_Carrying

Intangible Assets (Net Carrying Value) (Details) (USD $)	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Net carrying value of intangible assets	'	'	'	'	'	'
Goodwill	$120,164	'	$120,164	$113,414	'	'
Other intangible assets:	'	'	'	'	'	'
Total other intangible assets	13,865	'	15,388	10,243	'	'
Core deposit intangible assets [Member]	'	'	'	'	'	'
Other intangible assets:	'	'	'	'	'	'
Total other intangible assets	10,466	'	11,910	6,777	'	'
Mortgage servicing rights [Member]	'	'	'	'	'	'
Other intangible assets:	'	'	'	'	'	'
Total other intangible assets	$3,399	$3,421	$3,478	$3,466	$3,463	$3,593

Intangible_Assets_Amortization

Intangible Assets (Amortization Expense of Core Deposit Intangible Assets) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets	'	'	'	'	'
Carrying amount	$13,865	$10,243	$13,865	$10,243	$15,388
Amortization of intangible assets	'	'	2,794	2,935	'
Core deposit intangible assets [Member]	'	'	'	'	'
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets	'	'	'	'	'
Gross original amount	18,659	26,468	18,659	26,468	18,659
Accumulated amortization	8,193	19,691	8,193	19,691	6,749
Carrying amount	10,466	6,777	10,466	6,777	11,910
Amortization of intangible assets	$467	$367	$1,444	$1,102	'

Intangible_Assets_Carrying_and

Intangible Assets (Carrying and Fair Value of MSRs) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Net carrying value, fair value of MSRs and loans Corporation servicing for others	'	'	'
Loans serviced for others that have servicing rights capitalized	$886,980	$906,314	$901,052
Mortgage servicing rights [Member]	'	'	'
Net carrying value, fair value of MSRs and loans Corporation servicing for others	'	'	'
Net carrying value of MSRs	3,399	3,478	3,466
Fair value of MSRs	$6,839	$4,716	$4,277

Intangible_Assets_Activity_for

Intangible Assets (Activity for Capitalized MSRs) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Capitalized MSRs [Roll Forward]	'	'	'	'
Balance at beginning of period	'	'	$15,388	'
Amortization	'	'	-2,794	-2,935
Balance at end of period	13,865	10,243	13,865	10,243
Mortgage servicing rights [Member]	'	'	'	'
Capitalized MSRs [Roll Forward]	'	'	'	'
Balance at beginning of period	3,421	3,463	3,478	3,593
Additions	311	503	1,271	1,706
Amortization	-333	-500	-1,350	-1,833
Balance at end of period	$3,399	$3,466	$3,399	$3,466

Intangible_Assets_Textual_Deta

Intangible Assets (Textual) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Core deposit intangible assets [Member]	'	'	'
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]	'	'	'
2013	$500,000	'	'
2014	1,800,000	'	'
2015	1,700,000	'	'
2016	1,500,000	'	'
2017	1,200,000	'	'
2018 and thereafter	3,800,000	'	'
Mortgage servicing rights [Member]	'	'	'
Intangible Assets (Textual) [Abstract]	'	'	'
Impairment valuation allowance	$0	$0	$0

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Loss (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Components of accumulated other comprehensive loss, net of related tax benefit/expense	'	'	'
Net unrealized gains (losses) on investment securities – available-for-sale, net of related tax expense (benefit) of $(878) at September 30, 2013, $2,301 at December 31, 2012 and $2,542 at September 30, 2012	($1,631)	$4,274	$4,721
Pension and other postretirement benefits adjustment, net of related tax benefit of $18,062 at September 30, 2013, $19,058 at December 31, 2012 and $14,876 at September 30, 2012	-33,544	-35,393	-27,627
Accumulated other comprehensive loss	($35,175)	($31,119)	($22,906)

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Loss (Textual) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Accumulated Other Comprehensive Loss (Textual) [Abstract]	'	'	'
Net unrealized gains on investment securities-available-for-sale, tax expense	($878)	$2,301	$2,542
Pension and other postretirement benefits adjustment, tax benefit	$18,062	$19,058	$14,876

Regulatory_Capital_Details

Regulatory Capital (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]	'	'	'
Risk weighted assets	$4,510,000,000	$4,180,000,000	$4,030,000,000
Chemical Financial Corporation [Member]	'	'	'
Total Capital to Risk-Weighted Assets:	'	'	'
Actual, Capital Amount	638,786,000	552,171,000	549,388,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	361,199,000	334,140,000	322,212,000
Actual, Ratio	14.20%	13.20%	13.60%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%	8.00%
Tier 1 Capital to Risk-Weighted Assets:	'	'	'
Actual, Capital Amount	582,039,000	499,563,000	498,618,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	180,600,000	167,070,000	161,106,000
Actual, Ratio	12.90%	12.00%	12.40%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Leverage Ratio:	'	'	'
Actual, Capital Amount	582,039,000	499,563,000	498,618,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	232,972,000	217,145,000	211,670,000
Actual, Ratio	10.00%	9.20%	9.40%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Chemical Bank [Member]	'	'	'
Total Capital to Risk-Weighted Assets:	'	'	'
Actual, Capital Amount	568,626,000	536,223,000	537,467,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	360,617,000	333,195,000	321,585,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	450,771,000	416,494,000	401,982,000
Actual, Ratio	12.60%	12.90%	13.40%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%	8.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	10.00%	10.00%	10.00%
Tier 1 Capital to Risk-Weighted Assets:	'	'	'
Actual, Capital Amount	511,969,000	483,761,000	486,794,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	180,309,000	166,598,000	160,793,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	270,463,000	249,896,000	241,189,000
Actual, Ratio	11.40%	11.60%	12.10%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	6.00%	6.00%	6.00%
Leverage Ratio:	'	'	'
Actual, Capital Amount	511,969,000	483,761,000	486,794,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	232,828,000	216,784,000	211,452,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	$291,034,000	$270,980,000	$264,315,000
Actual, Ratio	8.80%	8.90%	9.20%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	5.00%	5.00%	5.00%

Regulatory_Capital_Common_Stoc

Regulatory Capital Common Stock Issued (Details) (USD $)	Sep. 30, 2013	Sep. 18, 2013	Dec. 31, 2012	Sep. 30, 2012
In Millions, except Share data, unless otherwise specified
Shares Issued [Abstract]	'	'	'	'
Common Stock, Shares, Issued	29,778,250	2,213,750	27,498,868	27,498,094
CommonStockIssuedOverAllotment	'	288,750	'	'
Shares Issued, Price Per Share	'	$26	'	'
Issuance of common stock, net of issuance costs	'	$53.90	'	'

Fair_Value_Measurements_Fair_V

Fair Value Measurements (Fair Value of Assets on a Recurring Basis) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	$705,146	$586,809	$646,578
Loans Receivable Held-for-sale, Net	'	17,665	15,075
Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	705,146	582,054	641,823
Loans Held-for-sale	7,907	17,665	15,075
Total assets measured at fair value on a recurring basis	713,053	599,719	656,898
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Loans Held-for-sale	0	0	0
Total assets measured at fair value on a recurring basis	0	0	0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	705,146	582,054	641,823
Loans Held-for-sale	'	17,665	'
Total assets measured at fair value on a recurring basis	713,053	599,719	656,898
Loans Receivable Held-for-sale, Net	7,907	'	15,075
Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Loans Held-for-sale	0	0	0
Total assets measured at fair value on a recurring basis	0	0	0
Government sponsored agencies [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	85,925	97,557	101,492
Government sponsored agencies [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	85,925	97,557	101,492
Government sponsored agencies [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Government sponsored agencies [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	85,925	97,557	101,492
Government sponsored agencies [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
State and political subdivisions [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	45,572	49,965	52,238
State and political subdivisions [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	45,572	49,965	52,238
State and political subdivisions [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
State and political subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	45,572	49,965	52,238
State and political subdivisions [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Residential mortgage-backed securities [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	308,160	99,411	105,236
Residential mortgage-backed securities [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	308,160	99,411	105,236
Residential mortgage-backed securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Residential mortgage-backed securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	308,160	99,411	105,236
Residential mortgage-backed securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Collateralized mortgage obligations [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	198,458	263,592	299,078
Collateralized mortgage obligations [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	198,458	263,592	299,078
Collateralized mortgage obligations [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Collateralized mortgage obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	198,458	263,592	299,078
Collateralized mortgage obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Corporate bonds [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	65,434	69,795	82,106
Corporate bonds [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	65,434	69,795	82,106
Corporate bonds [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Corporate bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	65,434	69,795	82,106
Corporate bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Preferred stock [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	1,597	6,489	6,428
Preferred stock [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	1,597	1,734	1,673
Preferred stock [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Preferred stock [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	1,597	1,734	1,673
Preferred stock [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	$0	$0	$0

Fair_Value_Measurements_Fair_V1

Fair Value Measurements (Fair Value of Assets on a Nonrecurring Basis) (Details) (Fair Value Measurements Nonrecurring [Member], USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	$51,568	$70,163	$73,372
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Significant Other Observable Inputs (Level 2) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Significant Unobservable Inputs (Level 3) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	51,568	70,163	73,372
Impaired originated loans [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	39,535	51,694	53,905
Impaired originated loans [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Impaired originated loans [Member] | Significant Other Observable Inputs (Level 2) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Impaired originated loans [Member] | Significant Unobservable Inputs (Level 3) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	39,535	51,694	53,905
Other real estate/repossessed assets [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	12,033	18,469	19,467
Other real estate/repossessed assets [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Other real estate/repossessed assets [Member] | Significant Other Observable Inputs (Level 2) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Other real estate/repossessed assets [Member] | Significant Unobservable Inputs (Level 3) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	$12,033	$18,469	$19,467

Fair_Value_Measurements_Schedu

Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Investment securities:	'	'	'
Available-for-sale	$705,146	$586,809	$646,578
Held-to-maturity	275,866	229,922	223,185
Carrying Amount [Member]	'	'	'
Investment securities:	'	'	'
Available-for-sale	0	4,755	4,755
Nonmarketable equity securities	25,572	25,572	25,572
Carrying Amount [Member] | Level 1[Member]	'	'	'
Assets:	'	'	'
Cash and cash equivalents	493,110	656,135	438,720
Carrying Amount [Member] | Level 2 [Member]	'	'	'
Investment securities:	'	'	'
Available-for-sale	705,146	582,054	641,823
Held-to-maturity	272,079	229,977	213,536
Loans Held-for-sale	7,907	17,665	15,075
Interest receivable	16,359	14,933	16,868
Liabilities:	'	'	'
Deposits without defined maturities	3,842,148	3,448,886	3,185,654
Interest payable	1,009	1,501	1,603
Short-term borrowings	357,595	310,463	311,471
FHLB advances	0	34,289	37,237
Carrying Amount [Member] | Level 3 [Member]	'	'	'
Investment securities:	'	'	'
Held-to-maturity	10,500	0	8,000
Net loans	4,441,139	4,083,244	3,934,465
Liabilities:	'	'	'
Time deposits	1,349,157	1,472,557	1,413,218
Fair Value [Member]	'	'	'
Investment securities:	'	'	'
Available-for-sale	0	4,755	4,755
Nonmarketable equity securities	25,572	25,572	25,572
Fair Value [Member] | Level 1[Member]	'	'	'
Assets:	'	'	'
Cash and cash equivalents	493,110	656,135	438,720
Fair Value [Member] | Level 2 [Member]	'	'	'
Investment securities:	'	'	'
Available-for-sale	705,146	582,054	641,823
Held-to-maturity	269,616	229,922	215,185
Loans Held-for-sale	7,907	17,665	15,075
Interest receivable	16,359	14,933	16,868
Liabilities:	'	'	'
Deposits without defined maturities	3,842,148	3,448,886	3,185,654
Interest payable	1,009	1,501	1,603
Short-term borrowings	357,595	310,463	311,471
FHLB advances	0	34,835	37,971
Fair Value [Member] | Level 3 [Member]	'	'	'
Investment securities:	'	'	'
Held-to-maturity	6,250	0	8,000
Net loans	4,446,796	4,093,880	3,951,313
Liabilities:	'	'	'
Time deposits	$1,359,739	$1,489,072	$1,432,493

Fair_Value_Measurements_Textua

Fair Value Measurements (Textual) (Details) (USD $)

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Core deposit intangible assets [Member]

Core deposit intangible assets [Member]

Core deposit intangible assets [Member]

Maximum [Member]

Minimum [Member]

Other Real Estate and Repossessed Assets [Member]

Other Real Estate and Repossessed Assets [Member]

Fair Value Measurements Recurring [Member]

Fair Value Measurements Recurring [Member]

Fair Value Measurements Recurring [Member]

Fair Value Measurements Nonrecurring [Member]

Fair Value Measurements Nonrecurring [Member]

Fair Value Measurements Nonrecurring [Member]

Maximum [Member]

Minimum [Member]

Fair Value Measurements (Textual) [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair Value of Trust Preferred Investment Securities

$6,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Liabilities recorded at fair value

'

'

'

'

'

'

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'

'

0

0

0

0

0

0

Expected life of intangible assets

'

'

'

'

'

'

'15 years

'10 years

'

'

'

'

'

'

'

'

Percentage of discount factors used to determine fair value

'

'

'

'

'

'

80.00%

70.00%

75.00%

70.00%

'

'

'

'

'

'

Impairment of goodwill

0

0

0

'

'

'

'

'

'

'

'

'

'

'

'

'

Impairment identified for intangible assets

'

'

'

$0

$0

$0

'

'

'

'

'

'

'

'

'

'

Earnings_Per_Common_Share_Deta

Earnings Per Common Share (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator and denominator of the basic and diluted earnings per common share computations	'	'	'	'
Numerator for both basic and diluted earnings per common share, net income	$14,993	$13,106	$42,430	$39,346
Denominator for basic earnings per common share, weighted average common shares outstanding	27,870,000	27,498,000	27,642,000	27,490,000
Weighted average common stock equivalents	167,000	90,000	144,000	78,000
Denominator for diluted earnings per common share	28,037,000	27,588,000	27,786,000	27,568,000
Basic earnings per common share (dollars per share)	$0.54	$0.48	$1.54	$1.43
Diluted earnings per common share (dollars per share)	$0.53	$0.48	$1.53	$1.43
Stock Option [Member]	'	'	'	'
Earnings Per Common Share (Textual) [Abstract]	'	'	'	'
Average number of exercisable employee stock option awards that were not included in the computation of diluted earnings per common share	308,009	611,605	377,847	618,703

ShareBased_Compensation_Stock_

Share-Based Compensation (Stock Option Activity) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]	'
Weighted average fair value of options granted	$7.40
Non Vested [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'
Ending balance, Number of Options	414,341
Vested [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'
Ending balance, Number of Options	1,134,513
Stock Options [Member] | Non Vested [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'
Beginning balance, Number of Options	314,765
Exercised, Number of Options	0
Vested, Number of Options	-126,682
Forfeited/expired, Number of Options	-17,961
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'
Beginning balance, Weighted Average Exercise Price	$23.03
Granted, Weighted Average Exercise Price	$25.14
Exercised, Weighted Average Exercise Price	$0
Vested, Weighted Average Exercise Price	$22.96
Forfeited/expired, Weighted Average Exercise Price	$23.34
Ending balance, Weighted Average Exercise Price	$24.28
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]	'
Beginning balance, Weighted average grant date fair value	$6.92
Weighted average fair value of options granted	$7.40
Exercised, Weighted Average Grant Date Fair Value	$0
Vested, Weighted Average Grant Date Fair Value	$6.93
Forfeited/expired, Weighted Average Grant Date Fair Value	$6.98
Ending balance, Weighted average grant date fair value	$7.19
Stock Options [Member] | Vested [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'
Beginning balance, Number of Options	997,222
Granted, Number of Options	244,219
Exercised, Number of Options	-87,842
Vested, Number of Options	0
Forfeited/expired, Number of Options	-19,086
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'
Beginning balance, Weighted Average Exercise Price	$27.24
Granted, Weighted Average Exercise Price	$25.14
Exercised, Weighted Average Exercise Price	$22.84
Vested, Weighted Average Exercise Price	$0
Forfeited/expired, Weighted Average Exercise Price	$24.07
Ending balance, Weighted Average Exercise Price	$27.19
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]	'
Exercisable/vested, Number of Options	720,172
Exercisable/vested, Weighted Average Exercise Price	$28.86

ShareBased_Compensation_BlackS

Share-Based Compensation (Black-Scholes Pricing Model Assumptions) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013
Assumptions of Black-Scholes option pricing model	'
Expected dividend yield	3.50%
Risk-free interest rate	1.34%
Expected stock price volatility	42.10%
Expected life of options - in years	'7 years 0 months 0 days
Weighted average fair value of options granted	$7.40

ShareBased_Compensation_Restri

Share-Based Compensation (Restricted Stock Unit Activity) (Details) (Restricted Stock Units (RSUs) [Member], USD $)	9 Months Ended
	Sep. 30, 2013
Restricted Stock Units (RSUs) [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Number of Shares [Roll Forward]	'
Beginning balance, Number of shares	156,510
Granted, Number of shares	71,429
Converted into shares of common stock, Number of shares	-36,172
Forfeited/expired, Number of shares	-3,330
Ending balance, Number of shares	188,437
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Weighted Average Grant Date Fair Value [Abstract]	'
Beginning balance, Weighted average grant date fair value	$20.83
Granted, Weighted Average grant date fair value	$23.41
Converted into shares of common stock, Weighted average grant date fair value	$22.47
Forfeited/expired, Weighted average grant date fair value	$21.67
Ending balance, Weighted average grant date fair value	$21.48

Textual_Details

(Textual) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Share-based compensation expense	'	'	$2,131,000	$1,305,000
Restricted Stock Units (RSUs) [Member]	'	'	'	'
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Share-based compensation expense	800,000	500,000	2,100,000	1,300,000
Corporation granted options to purchase restricted stock performance units	'	'	71,429	'
Unrecognized compensation expense	2,700,000	'	2,700,000	'
Unrecognized compensation expense, period of recognition	'	'	'2 years 2 months 12 days	'
Restricted Stock Units (RSUs) [Member] | Maximum [Member]	'	'	'	'
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Restricted stock performance units eligible to vest as a multiple of number of units granted	'	'	1.5	'
Restricted Stock Units (RSUs) [Member] | Minimum [Member]	'	'	'	'
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Restricted stock performance units eligible to vest as a multiple of number of units granted	'	'	0.25	'
Stock Option [Member]	'	'	'	'
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Corporation granted options to purchase common stock	'	'	244,219	'
Common stock available for future grants under share-based compensation plans	674,140	'	674,140	'
Weighted-average remaining contractual terms for outstanding stock options	'	'	'5 years 8 months 12 days	'
Weighted-average remaining contractual terms for exercisable stock options	'	'	'3 years 9 months 18 days	'
Outstanding in-the-money stock options, intrinsic value	3,300,000	'	3,300,000	'
Exercisable in-the-money stock options, intrinsic value	1,800,000	'	1,800,000	'
Closing price of common stock	$27.92	'	$27.92	'
Unrecognized compensation expense	2,400,000	'	2,400,000	'
Unrecognized compensation expense, period of recognition	'	'	'2 years 0 months 0 days	'
Parent Company [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Defined Contribution Plan, Employer Total Contribution Amount	$900,000	$800,000	$2,700,000	$2,300,000

Pension_and_Other_Postretireme2

Pension and Other Postretirement Benefit Plans (Components of Net Periodic Benefit Cost (Income)) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Defined Benefit Pension Plans [Member]	'	'	'	'
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan	'	'	'	'
Service cost	$326	$304	$976	$910
Interest cost	1,166	1,214	3,500	3,644
Expected return on plan assets	-1,949	-1,731	-5,845	-5,194
Amortization of prior service cost (credit)	0	0	-1	-1
Amortization of unrecognized net loss (gain)	946	614	2,838	1,843
Net periodic benefit cost (income)	489	401	1,468	1,202
Postretirement Benefit Plan [Member]	'	'	'	'
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan	'	'	'	'
Service cost	5	0	14	0
Interest cost	36	37	108	110
Amortization of prior service cost (credit)	27	-75	233	-225
Amortization of unrecognized net loss (gain)	-18	-7	-55	-21
Net periodic benefit cost (income)	$50	($45)	$300	($136)

Pension_and_Other_Postretireme3

Pension and Other Postretirement Benefit Plans (Textual) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Contribution to corporation's pension plan [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Contribution to defined benefit pension plan	'	'	$15	'
Pension Plans, Defined Benefit [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	'	'	4.08%	'
Chemical Financial Corporation [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Percentage of eligible pay contribution to certain employees	'	'	4.00%	'
Defined Contribution Plan, Employer Total Contribution Amount	$0.90	$0.80	$2.70	$2.30

Financial_Guarantees_Textual_D

Financial Guarantees (Textual) (Details) (Financial Standby Letter of Credit [Member], USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financial Standby Letter of Credit [Member]	'	'	'
Financial Guarantees (Textual) [Abstract]	'	'	'
Letters of credit outstanding	$48	$43	$43
Expiry of letters of credit, maximum	'5 years	'	'