Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	$ 1,023,124	$ 1,016,340
Total recurring fair value measurements	1,023,124	1,016,340
Loans held for sale	7,305	6,084
Total nonrecurring fair value measurements	18,548
Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	1,023,124	1,016,340
Nonrecurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Impaired loans	6,321	7,548
Other real estate owned and repossessed assets	3,918	3,029
Mortgage servicing rights fair value disclosure	1,004	1,311
Loans held for sale	7,305	6,084
Total nonrecurring fair value measurements		17,972
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	3,877
Total recurring fair value measurements	3,877	3,340
Loans held for sale
Total nonrecurring fair value measurements
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	3,877	3,340
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Nonrecurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Impaired loans
Other real estate owned and repossessed assets
Mortgage servicing rights fair value disclosure
Loans held for sale
Total nonrecurring fair value measurements
Significant Other Observable Inputs (Level 2) [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	1,019,223
Total recurring fair value measurements	1,019,223	1,012,953
Loans held for sale	7,305
Total nonrecurring fair value measurements	7,305
Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	1,019,223	1,012,953
Significant Other Observable Inputs (Level 2) [Member] | Nonrecurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Impaired loans
Other real estate owned and repossessed assets
Mortgage servicing rights fair value disclosure
Loans held for sale	7,305
Total nonrecurring fair value measurements
Significant Unobservable Inputs (Level 3) [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	24
Total recurring fair value measurements	24	47
Loans held for sale
Total nonrecurring fair value measurements	11,243
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	24	47
Significant Unobservable Inputs (Level 3) [Member] | Nonrecurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Impaired loans	6,321	7,548
Other real estate owned and repossessed assets	3,918	3,029
Mortgage servicing rights fair value disclosure	1,004	1,311
Loans held for sale		6,084
Total nonrecurring fair value measurements		17,972
Other Government Agencies [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	96,070	198,720
Other Government Agencies [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	96,070	198,720
Other Government Agencies [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value
Other Government Agencies [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	96,070	198,720
Other Government Agencies [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value
Residential mortgage-backed securities and collateralized mortgage obligations of government agencies [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	715,726	588,092
Residential mortgage-backed securities and collateralized mortgage obligations of government agencies [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	715,726	588,092
Residential mortgage-backed securities and collateralized mortgage obligations of government agencies [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value
Residential mortgage-backed securities and collateralized mortgage obligations of government agencies [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	715,726	588,092
Residential mortgage-backed securities and collateralized mortgage obligations of government agencies [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value
Obligations of States and Political Subdivisions [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	167,181	180,433
Obligations of States and Political Subdivisions [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	167,181	180,433
Obligations of States and Political Subdivisions [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value
Obligations of States and Political Subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	167,157	180,386
Obligations of States and Political Subdivisions [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	24	47
Corporate Debt Securities [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	38,570	44,066
Corporate Debt Securities [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	38,570	44,066
Corporate Debt Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value
Corporate Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	38,570	44,066
Corporate Debt Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value
Equity Securities [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	5,577	5,029
Equity Securities [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	5,577	5,029
Equity Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	3,877	3,340
Equity Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value	1,700	1,689
Equity Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Available-for-sale, at fair value