Debt - Adoption of ASU (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Jan. 01, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Convertible senior notes, net	$ 811,068			$ 378,586
Total liabilities	1,365,883			841,586
Additional paid-in capital	591,529			692,603
Accumulated deficit	(691,403)			(617,279)
Total stockholders' equity	(105,003)	$ (95,395)		71,536	$ 85,353	$ 90,688	$ 83,168
Total liabilities and stockholders' equity	$ 1,260,880			913,122
Cumulative Effect, Period of Adoption, Adjustment
Debt Instrument [Line Items]
Total stockholders' equity				$ (71,441)
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2020-06
Debt Instrument [Line Items]
Convertible senior notes, net			$ 71,441
Total liabilities			71,441
Additional paid-in capital			(99,026)
Accumulated deficit			27,585
Total stockholders' equity			(71,441)
Total liabilities and stockholders' equity			0
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2020-06, Transfer Equity Component of the Debt to Liabilities
Debt Instrument [Line Items]
Convertible senior notes, net			102,166
Total liabilities			102,166
Additional paid-in capital			(102,166)
Accumulated deficit			0
Total stockholders' equity			(102,166)
Total liabilities and stockholders' equity			0
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2020-06, Equity Component of Debt Issuance Costs
Debt Instrument [Line Items]
Convertible senior notes, net			(3,140)
Total liabilities			(3,140)
Additional paid-in capital			3,140
Accumulated deficit			0
Total stockholders' equity			3,140
Total liabilities and stockholders' equity			0
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2020-06, Reverse Debt Discount Amortization
Debt Instrument [Line Items]
Convertible senior notes, net			(28,811)
Total liabilities			(28,811)
Additional paid-in capital			0
Accumulated deficit			28,811
Total stockholders' equity			28,811
Total liabilities and stockholders' equity			0
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2020-06, Record Debt Issuance Costs Amortization
Debt Instrument [Line Items]
Convertible senior notes, net			1,226
Total liabilities			1,226
Additional paid-in capital			0
Accumulated deficit			(1,226)
Total stockholders' equity			(1,226)
Total liabilities and stockholders' equity			0
Cumulative Effect, Period of Adoption, Adjusted Balance | Accounting Standards Update 2020-06
Debt Instrument [Line Items]
Convertible senior notes, net			450,027
Total liabilities			913,027
Additional paid-in capital			593,577
Accumulated deficit			(589,694)
Total stockholders' equity			95
Total liabilities and stockholders' equity			$ 913,122