Newly Issued Accounting Standards (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity	$ 118,880	$ 136,504	$ 162,266	$ 182,125	$ 32,067	$ (29,199)
Additional paid-in capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity	544,094	542,093	566,916	615,207	497,249	434,391
Accumulated deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity	(403,453)	$ (383,872)	(384,187)	$ (361,206)	$ (392,080)	$ (391,215)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity			(12,939)
Book value of long-term debt			12,939
Cumulative Effect, Period of Adoption, Adjustment | Additional paid-in capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity			(26,699)
Cumulative Effect, Period of Adoption, Adjustment | Accumulated deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity			13,760
Senior Notes
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Book value of long-term debt	$ 141,774		$ 128,210
4.50% Exchangeable Senior Notes Due 2023 | Senior Notes
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt instrument, interest rate, stated percentage	4.50%		4.50%