Fair Market Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 603,033	$ 605,394		$ 603,033		$ 605,394
Reconciliation of beginning and ending balances of recurring fair value measurements recognized in balance sheet using significant unobservable (Level 3) inputs [Roll Forward]
Total losses	(119)		$ 0	$ (419)	$ (660)
Minimum [Member]
Other real estate owned [Abstract]
Typical frequency of periodic reviews				12 months
Maximum [Member]
Other real estate owned [Abstract]
Typical frequency of periodic reviews				18 months
Frequency of periodic reviews in general				24 months
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	89,613	69,292		$ 89,613		69,292
Significant Other Observable Inputs (Level 2) [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	513,420	536,102		513,420		536,102
Significant Unobservable Inputs (Level 3) [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0		0		0
Recurring [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights	3,283	3,433		3,283		3,433
Recurring [Member] | Fair Value [Member] | U.S. Treasury and Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	217,858	222,464		217,858		222,464
Recurring [Member] | Fair Value [Member] | State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	136,657	133,516		136,657		133,516
Recurring [Member] | Fair Value [Member] | U.S. Government Sponsored Agency Mortgage-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	223,998	225,056		223,998		225,056
Recurring [Member] | Fair Value [Member] | CRA Investments Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	24,520	24,358		24,520		24,358
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights	0	0		0		0
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value [Member] | U.S. Treasury and Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	65,093	44,934		65,093		44,934
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value [Member] | State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0		0		0
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value [Member] | U.S. Government Sponsored Agency Mortgage-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0		0		0
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value [Member] | CRA Investments Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	24,520	24,358		24,520		24,358
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights	0	0		0		0
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value [Member] | U.S. Treasury and Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	152,765	177,530		152,765		177,530
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value [Member] | State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	136,657	133,516		136,657		133,516
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value [Member] | U.S. Government Sponsored Agency Mortgage-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	223,998	225,056		223,998		225,056
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value [Member] | CRA Investments Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0		0		0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights	3,283	3,433		3,283		3,433
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value [Member] | U.S. Treasury and Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0		0		0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value [Member] | State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0		0		0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value [Member] | U.S. Government Sponsored Agency Mortgage-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0		0		0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value [Member] | CRA Investments Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0		0		0
Recurring [Member] | Mortgage Servicing Rights [Member]
Reconciliation of beginning and ending balances of recurring fair value measurements recognized in balance sheet using significant unobservable (Level 3) inputs [Roll Forward]
Beginning balance	3,304	2,964	2,797	3,433	3,236	3,236
Total recognized gains (losses) Included in net income	5		118	(73)	(422)
Issues	98		167	269	388
Settlements	(124)		(118)	(346)	(238)
Ending balance	3,283	3,433	2,964	3,283	2,964	3,433
Total gains (losses) for the period included in net income attributable to the change in unrealized gains or losses related to assets still held at the reporting date	5		118	(73)	(422)
Nonrecurring [Member]
Impaired loan (collateral dependent) [Abstract]
Impaired loans, fair value adjustments	300	300	300	700	600	600
Other real estate owned [Abstract]
Other real estate /assets owned, fair value adjustment	900	600	$ 400	2,900	$ 600	1,200
Nonrecurring [Member] | Fair Value [Member]
Assets measured-nonrecurring basis [Abstract]
Impaired loans (collateral dependent)	1,732	5,506		1,732		5,506
Other real estate /assets owned	18,843	4,388		18,843		4,388
Nonrecurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value [Member]
Assets measured-nonrecurring basis [Abstract]
Impaired loans (collateral dependent)	0	0		0		0
Other real estate /assets owned	0	0		0		0
Nonrecurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value [Member]
Assets measured-nonrecurring basis [Abstract]
Impaired loans (collateral dependent)	0	0		0		0
Other real estate /assets owned	0	0		0		0
Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value [Member]
Assets measured-nonrecurring basis [Abstract]
Impaired loans (collateral dependent)	1,732	5,506		1,732		5,506
Other real estate /assets owned	$ 18,843	$ 4,388		$ 18,843		$ 4,388