Investment and Mortgage-Backed Securities, Available for Sale (Schedule of Available for Sale Securities) (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Losses	$ 67,000
Available For Sale Securities Pledged as Collateral, Amortized Cost Basis	117,700,000		$ 99,200,000
Available-for-sale Securities Pledged as Collateral, Fair Value	118,000,000		100,500,000
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	358,328,622		380,374,568
Available-for-sale Securities, Gross Unrealized Gains	3,336,066		5,840,528
Available-for-sale Securities, Gross Unrealized Losses	2,812,488		1,241,190
Available-for-sale Securities, Fair Value Disclosure	358,852,200		384,973,906
Proceeds From Sale of Available For Sale Securities Including Mortgage Backed Securities	28,600,000	$ 15,300,000
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	57,866,536		59,623,185
Available-for-sale Securities, Gross Unrealized Gains	1,231,282		2,789,233
Available-for-sale Securities, Gross Unrealized Losses	445,775		56,851
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	30,300,000		26,900,000
Available-for-sale Securities, Fair Value Disclosure			26,900,000
Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains	503,000	$ 583,000
SBA Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	116,226,896		123,324,802
Available-for-sale Securities, Gross Unrealized Gains	914,781		1,113,160
Available-for-sale Securities, Gross Unrealized Losses	328,335		189,518
Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	170,554,894		186,732,705
Available-for-sale Securities, Gross Unrealized Gains	1,178,301		1,936,847
Available-for-sale Securities, Gross Unrealized Losses	1,914,324		973,572
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	155,000		155,000
Available-for-sale Securities, Gross Unrealized Gains	0		0
Available-for-sale Securities, Gross Unrealized Losses	0		0
Taxable Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	2,015,694		2,016,833
Available-for-sale Securities, Gross Unrealized Gains	0		0
Available-for-sale Securities, Gross Unrealized Losses	34,364		19,703
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair Value Disclosure	58,652,043		62,355,567
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| SBA Bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair Value Disclosure	116,813,342		124,248,444
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair Value Disclosure	169,818,871		187,695,980
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair Value Disclosure	155,000		155,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Taxable Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair Value Disclosure	$ 1,981,330		$ 1,997,130

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Proceeds From Sale of Available For Sale Securities Including Mortgage Backed Securities

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

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