Notes Payable (Details) (USD $)	12 Months Ended		12 Months Ended			12 Months Ended			1 Months Ended		1 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2012 Term loans under secured credit facility	Dec. 31, 2011 Term loans under secured credit facility	Jan. 31, 2011 Term loans under secured credit facility	Dec. 31, 2012 Term loans under secured credit facility Before the amortization date	Dec. 31, 2012 Term loans under secured credit facility 15-month period after the amortization date	Dec. 31, 2012 Term loans under secured credit facility Thereafter	Jan. 31, 2011 Initial term loan facility	Dec. 31, 2012 Initial term loan facility	Dec. 31, 2011 Additional term loan after amendment	Dec. 31, 2012 Additional term loan after amendment
Notes payable
Aggregate amount				$ 30,000,000
Draw down under secured credit facility	30,000,000								15,000,000		15,000,000
Fixed interest rate (as a percent)										11.00%		11.00%
Required principal payments
2013		11,809,000
2014		10,847,000
2015		569,000
Total		23,225,000
Prepayment premium (as a percent)						5.00%	2.00%	1.00%
Final payment required to be made as a percentage of aggregate principal amount			2.50%
Final payment required to be made			750,000
Accrued amount related to final payment			300,000	100,000
Financing costs capitalized			233,000	378,000	498,000
Debt discount			328,000	514,000
Interest expense			2,900,000	1,500,000
Amortization of debt discount			$ 600,000	$ 300,000