Convertible Senior Notes - Summary of Total Interest Expense Recognized Related To Convertible Senior Notes (Details) - Convertible Senior Notes - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Amortization of debt discount and transaction costs	$ 1,243	$ 1,160	$ 3,667	$ 3,435
Total interest expense	1,672	1,592	4,961	4,736
1.50% Coupon
Debt Instrument [Line Items]
Interest expense	$ 429	$ 432	$ 1,294	$ 1,301