Fair Value (Schedule of Financial Instruments Utilizing Level 3 Inputs) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Residential Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 100,911,651	$ 76,473,092
Total net transfers into/out of Level 3
Acquisitions	175,559,950	68,617,460
Proceeds from sales		(43,379,205)
Net accretion of discounts	960,203	(1,337,369)
Proceeds from principal repayments	5,938,134	(16,938,626)
Total losses (realized / unrealized) included in earnings	(271,607)	2,579,401
Total gains (realized / unrealized) included in earnings	2,417,721	17,380,962
Ending balance	273,639,784	100,911,651
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets or liabilities still held at the reporting date	2,146,115	10,764,268
Mortgage loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance
Total net transfers into/out of Level 3
Acquisitions	10,868,715
Proceeds from sales
Net accretion of discounts	28,906
Proceeds from principal repayments
Total losses (realized / unrealized) included in earnings	(28,906)
Total gains (realized / unrealized) included in earnings
Ending balance	10,839,809
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets or liabilities still held at the reporting date	$ (28,906)