Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2009	$ 474,311	$ 23,891	$ 347,676	$ 115,391	$ (12,647)
Changes in Stockholders' Equity [Roll Forward]
Comprehensive income	21,626			23,090	(1,464)
Cash dividends declared per share: $0.80 per share in 2010, $0.80 per share in 2011 and $0.82 per share in 2012	(21,243)			(21,243)
Stock issued - stock options	42	1	41
Shares and stock options issued in the acquisition of O.A.K. Financial Corporation	83,697	3,530	80,167
Shares issued - directors' stock plans	250	12	238
Share-based compensation	1,395	6	1,389
Ending Balance at Dec. 31, 2010	560,078	27,440	429,511	117,238	(14,111)
Changes in Stockholders' Equity [Roll Forward]
Comprehensive income	31,832			43,050	(11,218)
Cash dividends declared per share: $0.80 per share in 2010, $0.80 per share in 2011 and $0.82 per share in 2012	(21,964)			(21,964)
Shares issued - directors' stock plans	266	12	254
Share-based compensation	1,517	5	1,512
Ending Balance at Dec. 31, 2011	571,729	27,457	431,277	138,324	(25,329)
Changes in Stockholders' Equity [Roll Forward]
Comprehensive income	45,218			51,008	(5,790)
Cash dividends declared per share: $0.80 per share in 2010, $0.80 per share in 2011 and $0.82 per share in 2012	(22,566)			(22,566)
Stock issued - stock options		1	19
Shares issued - directors' stock plans	323	16	307
Shares issued — restricted stock performance units	(248)	25	(273)
Share-based compensation	1,865		1,865
Ending Balance at Dec. 31, 2012	$ 596,341	$ 27,499	$ 433,195	$ 166,766	$ (31,119)

This element represents the amount of recognized equity-based compensation during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized). Alternate captions include the words "stock-based compensation".

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 20

-Section 55

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6576910&loc=d3e11178-113907

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 35

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415241&loc=d3e4534-113899

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A91

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 20

-Section 55

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6576910&loc=d3e11149-113907

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 39

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to the reporting entity. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, but excludes any and all transactions which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.

+ References+ Details

- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

+ References+ Details

- Definition

Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

+ References+ Details

- Definition

Value of stock related to Restricted Stock Awards issued during the period, net of the stock value of such awards forfeited.

+ References+ Details

- Definition

Value of stock issued as a result of the exercise of stock options.

+ References+ Details