Long-Term Debt - Narrative (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Feb. 16, 2018 USD ($) day $ / shares Rate	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Schedule of Capitalization, Long-term Debt [Line Items]
Proceeds from loans or conditional grants		$ 0	$ 0	$ 143,750
ADSs, conversion ratio | Rate	9269.56%
4.50% Exchangeable Senior Notes Due 2023
Schedule of Capitalization, Long-term Debt [Line Items]
Interest rate		4.50%
4.50% Exchangeable Senior Notes Due 2023 | Convertible Debt
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, face amount	$ 125,000
Interest rate	4.50%
Option to increase aggregate principal amount	$ 18,750
Proceeds from loans or conditional grants	$ 137,560
ADS, option price per share (in dollars per share) | $ / shares	$ 10.79
ADS premium percentage	20.00%
ADS purchased, price per share (in dollars per share) | $ / shares	$ 8.99
Debt Instrument, Redemption, Period One | 4.50% Exchangeable Senior Notes Due 2023 | Convertible Debt
Schedule of Capitalization, Long-term Debt [Line Items]
Number of business days	5 days
Consecutive business days	5 days
Percentage of product of the last reported sale price of the American Depositary Shares and the exchange rate on each such trading day	98.00%
Debt Instrument, Redemption, Period Two | 4.50% Exchangeable Senior Notes Due 2023 | Convertible Debt
Schedule of Capitalization, Long-term Debt [Line Items]
Scheduled threshold trading days	95 days
Threshold trading days | day	35
Debt Instrument, Redemption, Period Three | 4.50% Exchangeable Senior Notes Due 2023 | Convertible Debt
Schedule of Capitalization, Long-term Debt [Line Items]
Threshold trading days | day	20
Consecutive trading days | day	30
Threshold percentage of stock price trigger	130.00%