Fair Value Measurement (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	$ 993,270	$ 1,021,244
Loans held for sale	14,299	21,903
Recurring fair value measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	993,270	1,021,244
Total recurring fair value measurements	993,270	1,021,244
Nonrecurring fair value measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Impaired loans	3,792	3,866
Other real estate owned and repossessed assets	5,147	5,988
Mortgage servicing rights	693	825
Loans held for sale	14,299	21,903
Total nonrecurring fair value measurements	23,931	32,582
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
Total securities - available-for-sale	8,986	9,059
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
Total securities - available-for-sale	8,986	9,059
Total recurring fair value measurements	8,986	9,059
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
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
Total securities - available-for-sale	984,284	1,012,162
Loans held for sale	14,299	21,903
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
Total securities - available-for-sale	984,284	1,012,162
Total recurring fair value measurements	984,284	1,012,162
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
Loans held for sale	14,299	21,903
Total nonrecurring fair value measurements	14,299	21,903
Significant Unobservable Inputs (Level 3) [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale		23
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
Total securities - available-for-sale		23
Total recurring fair value measurements		23
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	3,792	3,866
Other real estate owned and repossessed assets	5,147	5,988
Mortgage servicing rights	693	825
Loans held for sale
Total nonrecurring fair value measurements	9,632	10,679
Other government agencies [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	65,449	96,612
Other government agencies [Member] | Recurring fair value measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	65,449	96,612
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
Total securities - available-for-sale
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
Total securities - available-for-sale	65,449	96,612
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
Total securities - available-for-sale
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
Total securities - available-for-sale	738,942	732,210
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
Total securities - available-for-sale	738,942	732,210
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
Total securities - available-for-sale
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
Total securities - available-for-sale	738,942	732,210
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
Total securities - available-for-sale
Obligations of state and political subdivisions [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	139,620	148,635
Obligations of state and political subdivisions [Member] | Recurring fair value measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	139,620	148,635
Obligations of state 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
Total securities - available-for-sale
Obligations of state 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
Total securities - available-for-sale	139,620	148,612
Obligations of state 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
Total securities - available-for-sale		23
Corporate debt securities [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	38,136	32,685
Corporate debt securities [Member] | Recurring fair value measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	38,136	32,685
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
Total securities - available-for-sale
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
Total securities - available-for-sale	38,136	32,685
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
Total securities - available-for-sale
Equity securities [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	11,123	11,102
Equity securities [Member] | Recurring fair value measurements [Member]
Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis
Total securities - available-for-sale	11,123	11,102
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
Total securities - available-for-sale	8,986	9,059
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
Total securities - available-for-sale	2,137	2,043
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
Total securities - available-for-sale