Debt (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Interest expense on convertible senior notes
Convertible senior notes, contractual interest expense	$ 718	$ 399	$ 2,148	$ 399
Amortization of debt issuance costs	319	213	958	213
Amortization of debt discount	2,792	1,483	8,315	1,483
Convertible senior notes, total interest expense	$ 3,829	$ 2,095	$ 11,421	$ 2,095
Convertible senior notes, effective interest rate during period	6.50%	6.60%	6.50%	6.60%