MBS Investments Terms of MBS (Details) (Trust Portfolio--MBS Bonds [Member], USD $)	12 Months Ended
	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, not Including Premiums	$ 31,620,000
Standard & Poor's, AA Rating [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Instrument, Credit Rating	"AA"
Available for Sale Securities, not Including Premiums	18,945,000
Debt Instrument, Maturity Date	Jan. 18, 2036
Debt, Weighted Average Interest Rate	4.00%
Standard & Poor's, AAA Rating [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Instrument, Credit Rating	"AAA"
Available for Sale Securities, not Including Premiums	$ 12,675,000
Debt Instrument, Maturity Date	Jan. 14, 2036
Debt, Weighted Average Interest Rate	4.22%