Fair Value Measurements Fair Value of Assets (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Assets, Fair Value Disclosure	$ 137,389,392		$ 137,389,392			$ 137,018,622
Gain on sale of bonds	667,821	0	667,821	0
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities			95,000	0
Tax-exempt mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets, Fair Value Disclosure	136,846,619		136,846,619			135,695,352
Interest rate derivatives [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets, Fair Value Disclosure	542,773		542,773			1,323,270
Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	10,164,815	15,625,000	10,164,815	20,117,500
Assets, Fair Value Disclosure	137,389,392	139,824,045	137,389,392	139,824,045	139,570,108	137,018,622	111,101,801	103,973,434
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	137,389,392		137,389,392			137,018,622
Gain on sale of bonds	(451,157)	(656,000)	(780,497)	(888,554)
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	(15,625,000)	(5,795,000)	(15,625,000)	(5,047,208)
Fair Value, Inputs, Level 3 [Member] | Tax-exempt mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	10,164,815	15,625,000	10,164,815	20,117,500
Assets, Fair Value Disclosure	136,846,619	137,305,808	136,846,619	137,305,808	138,576,178	135,695,352	107,927,564	100,566,643
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	136,846,619		136,846,619			135,695,352
Gain on sale of bonds	0	0	0	0
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	(15,625,000)	(5,795,000)	(15,625,000)	(5,047,208)
Fair Value, Inputs, Level 3 [Member] | Interest rate derivatives [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0		0
Assets, Fair Value Disclosure	542,773	2,518,237	542,773	2,518,237	993,930	1,323,270	3,174,237	3,406,791
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	542,773		542,773			1,323,270
Gain on sale of bonds	(451,157)	(656,000)	(780,497)	(888,554)
Unrealized Gain (Loss) on Investments			(780,497)
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	0		0
Fair Value, Inputs, Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Method Investment, Quoted Market Value	0		0			0
Fair Value, Inputs, Level 1 [Member] | Tax-exempt mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Method Investment, Quoted Market Value	0		0			0
Fair Value, Inputs, Level 1 [Member] | Interest rate derivatives [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Method Investment, Quoted Market Value	0		0			0
Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Observable inputs (level 2)	0		0			0
Fair Value, Inputs, Level 2 [Member] | Tax-exempt mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Observable inputs (level 2)	0		0			0
Fair Value, Inputs, Level 2 [Member] | Interest rate derivatives [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Observable inputs (level 2)	$ 0		$ 0			$ 0