Investment and Mortgage-Backed Securities, Available for Sale (Narrative) (Details)	3 Months Ended
	Mar. 31, 2017 USD ($) security	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	$ 379,045,853		$ 360,457,164
Available-for-sale Securities, Fair Value Disclosure	381,474,385		362,059,429
Available For Sale Securities Pledged as Collateral, Amortized Cost Basis	94,800,000		75,300,000
Available-for-sale Securities Pledged as Collateral, Fair Value	96,400,000		$ 76,900,000
Proceeds From Sale of Available For Sale Securities Including Mortgage Backed Securities	$ 15,300,000	$ 3,200,000
Percent of unrealized losses for securities in a continuous loss position for 12 months or more	7.00%		3.50%
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	21		15
Available-for-sale Securities, Gross Realized Losses	$ 0
GNMA Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	96,800,000		$ 107,900,000
Available-for-sale Securities, Fair Value Disclosure	97,900,000		109,200,000
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	20,100,000		20,000,000
Available-for-sale Securities, Fair Value Disclosure	19,900,000		$ 19,700,000
Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains	$ 583,000	$ 258,000