Fair Value Measurements (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($) Fund	Dec. 31, 2016 USD ($)
Fair Value Disclosures [Abstract]
Number of mutual funds that invest in debt securities or loans that qualify for credit under the Community Reinvestment Act (in fund) | Fund	5
Number of investments in mutual funds that are measured at fair value using net asset value per share as a practical expedient (in investments) | Fund	2
Number Of Investments In Mutual Funds That Are Measured At Fair Value Using Market Quotations | Fund	2
Redemption notice required to be given to convert capital account, number of days	60 days
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	$ 310,404	$ 320,659
Recurring [Member]
Recurring fair value measurement [Abstract]
Total recurring fair value measurements	310,404	320,659
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Recurring fair value measurement [Abstract]
Total recurring fair value measurements	16,875	28,870
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Recurring fair value measurement [Abstract]
Total recurring fair value measurements	292,012	290,307
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Recurring fair value measurement [Abstract]
Total recurring fair value measurements	0	0
Nonrecurring [Member]
Nonrecurring fair value measurements:
Impaired loans	3,712	5,340
Nonrecurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Nonrecurring fair value measurements:
Impaired loans	0	0
Nonrecurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Nonrecurring fair value measurements:
Impaired loans	0	0
Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Nonrecurring fair value measurements:
Impaired loans	3,712	5,340
U.S. Treasury notes [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	16,152	28,145
U.S. Treasury notes [Member] | Recurring [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	16,152	28,145
U.S. Treasury notes [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	16,152	28,145
U.S. Treasury notes [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
U.S. Treasury notes [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
U.S. Agency notes [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	86,946	85,400
U.S. Agency notes [Member] | Recurring [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	86,946	85,400
U.S. Agency notes [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
U.S. Agency notes [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	86,946	85,400
U.S. Agency notes [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
U.S. Agency mortgage-backed securities [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	70,721	71,047
U.S. Agency mortgage-backed securities [Member] | Recurring [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	70,721	71,047
U.S. Agency mortgage-backed securities [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
U.S. Agency mortgage-backed securities [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	70,721	71,047
U.S. Agency mortgage-backed securities [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
Non-taxable Municipal securities [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	110,723	113,015
Non-taxable Municipal securities [Member] | Recurring [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	110,723	113,015
Non-taxable Municipal securities [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
Non-taxable Municipal securities [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	110,723	113,015
Non-taxable Municipal securities [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
Taxable Municipal securities [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	22,622	19,845
Taxable Municipal securities [Member] | Recurring [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	22,622	19,845
Taxable Municipal securities [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
Taxable Municipal securities [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	22,622	19,845
Taxable Municipal securities [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
Mutual funds [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	2,539	2,482
Mutual funds [Member] | Recurring [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	1,022	1,000
Mutual funds [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	22	0
Mutual funds [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	1,000	1,000
Mutual funds [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
Mutual funds measured at net asset value [Member] | Recurring [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	1,517	1,482
Trust preferred securities [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	50	48
Trust preferred securities [Member] | Recurring [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	50	48
Trust preferred securities [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	50	48
Trust preferred securities [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
Trust preferred securities [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
Equity securities [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	651	677
Equity securities [Member] | Recurring [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	651	677
Equity securities [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	651	677
Equity securities [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	0	0
Equity securities [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Recurring fair value measurement [Abstract]
Available-for-sale, at fair value	$ 0	$ 0