Repurchase Agreements - Maturities (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	$ 109,863,000	$ 46,788,000
Repurchase agreements	103,941,174	44,325,000
Net weighted average borrowing rate	0.49%	0.44%
[MaturityOvernightMember]
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	0	0
Repurchase agreements	0	0
Net weighted average borrowing rate	0.00%	0.00%
[MaturityUpTo30DaysMember]
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	109,863,000	46,788,000
Repurchase agreements	103,941,000	44,325,000
Net weighted average borrowing rate	0.49%	0.44%
[Maturity30To90DaysMember]
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	0	0
Repurchase agreements	0	0
Net weighted average borrowing rate	0.00%	0.00%
[MaturityOver90DaysMember]
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	0	0
Repurchase agreements	$ 0	$ 0
Net weighted average borrowing rate	0.00%	0.00%