Mortgage-Backed Securities Terms of MBS Securities (Details) - Trust Portfolio M B S Bonds	12 Months Ended
	Dec. 31, 2015 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Principal Outstanding	$ 14,765,000
Standard & Poor's, AAA Rating [Member]
Schedule Of Available For Sale Securities [Line Items]
Debt Instrument, Credit Rating	“AAA”	[1]
Principal Outstanding	$ 5,000,000
Debt Instrument, Weighted Average Maturity Date	Jul. 01, 2032
Debt, Weighted Average Interest Rate	4.60%
Standard & Poor's, AA Rating [Member]
Schedule Of Available For Sale Securities [Line Items]
Debt Instrument, Credit Rating	“AA”	[1]
Principal Outstanding	$ 9,765,000
Debt Instrument, Weighted Average Maturity Date	Jul. 09, 2036
Debt, Weighted Average Interest Rate	4.20%

[1] MBS Securities are reported based on the lowest rating issued by a Rating Agency, if more than one rating is issued on the security, at the date presented.