Convertible Notes and Credit Facilities - Convertible Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Debt Disclosure [Abstract]
Principal amount	$ 128,250	$ 128,250	$ 128,250
Less: Debt discount, net of amortization	(11,996)	(17,404)
Less: Debt issuance costs, net of amortization	(1,446)	(2,098)
Carrying amount	$ 114,808	$ 108,748
Remaining amortization period (years)	1 year 10 months 28 days	2 years 10 months 28 days
Effective interest rate on liability component	9.94%	9.94%
Carrying amount of equity component	$ 26,062	$ 26,062