Securities - Amortized Cost to Approximate Fair Value (Details) - USD ($)	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Trading Securities
Unrealized gains included in trading securities	$ 661,000	$ 1,400,000
Available-for-sale securities:
Amortized Cost	271,433,000		$ 410,062,000
Gross Unrealized Gains	3,000
Gross Unrealized Losses	1,727,000		1,691,000
Fair Value	269,709,000		408,371,000
Treasury notes
Available-for-sale securities:
Amortized Cost	3,489,000		1,000,000
Gross Unrealized Losses	24,000		8,000
Fair Value	3,465,000		992,000
Federal agencies
Available-for-sale securities:
Amortized Cost	242,247,000		376,414,000
Gross Unrealized Losses	1,703,000		1,683,000
Fair Value	240,544,000		374,731,000
Equities
Available-for-sale securities:
Amortized Cost	69,000
Gross Unrealized Gains	3,000
Fair Value	72,000
Municipals
Available-for-sale securities:
Amortized Cost			6,688,000
Fair Value			6,688,000
Mortgage-backed - Government-sponsored entity (GSE) - residential
Available-for-sale securities:
Amortized Cost	25,628,000		25,960,000
Fair Value	$ 25,628,000		$ 25,960,000

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of unrealized holding gain (loss) recognized in the income statement for investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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