Investment and Mortgage-Backed Securities, Available for Sale (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) security	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) security	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	$ 395,298,490		$ 395,298,490		$ 360,457,164
Available-for-sale Securities, Fair Value Disclosure	401,349,864		401,349,864		362,059,429
Available For Sale Securities Pledged as Collateral, Amortized Cost Basis	92,100,000		92,100,000		75,300,000
Available-for-sale Securities Pledged as Collateral, Fair Value	93,900,000		93,900,000		$ 76,900,000
Proceeds From Sale of Available For Sale Securities Including Mortgage Backed Securities	$ 2,200,000	$ 11,400,000	$ 17,500,000	$ 14,600,000
Percent of unrealized losses for securities in a continuous loss position for 12 months or more	25.40%		25.40%		3.50%
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	21		21		15
Available-for-sale Securities, Gross Realized Losses	$ 0		$ 0
GNMA Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	101,100,000		101,100,000		$ 107,900,000
Available-for-sale Securities, Fair Value Disclosure	102,400,000		102,400,000		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	29,700,000		29,700,000		20,000,000
Available-for-sale Securities, Fair Value Disclosure	29,700,000		29,700,000		$ 19,700,000
Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains	$ 45,000	$ 154,000	$ 629,000	$ 412,000