Prepaid expenses and other assets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Prepaid expenses and other assets
Interest receivable	$ 743	$ 725
Prepaid insurance	6,979	672
Prepaid sales and marketing expenses	5,735
Prepaid medical affairs expenses	1,782
Manufacturing capacity commitment fees	2,300
Other prepaid expenses and assets	1,907	396
Total	$ 19,446	$ 1,793