Notes Payable (Details) (USD $)	3 Months Ended						3 Months Ended			1 Months Ended		1 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Term loans under secured credit facility	Mar. 31, 2012 Term loans under secured credit facility	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	Mar. 31, 2013 Term loans under secured credit facility Before the amortization date	Mar. 31, 2013 Term loans under secured credit facility 15-month period after the amortization date	Mar. 31, 2013 Term loans under secured credit facility Thereafter	Jan. 31, 2011 Initial term loan facility	Mar. 31, 2013 Initial term loan facility	Dec. 31, 2011 Additional term loan after amendment	Mar. 31, 2013 Additional term loan after amendment	May 03, 2013 7.50% Convertible Senior Secured Notes due 2019
Notes payable
Aggregate amount					$ 30,000,000
Draw down under secured credit facility	90,000,000									15,000,000		15,000,000
Fixed interest rate (as a percent)	7.50%										11.00%		11.00%	7.50%
Required principal payments
2013		8,977,000
2014		10,847,000
2015		569,000
Total		20,393,000
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		388,000		330,000
Financing costs capitalized		209,000		233,000		498,000
Debt discount		281,000		328,000
Interest expense		587,000	821,000
Amortization of debt discount		$ 141,000	$ 141,000