Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income (loss)	$ (12,066)	$ (12,779)	$ (10,781)	$ (7,983)	$ (9,532)	$ (17,331)	$ (36,980)	$ (26,576)	$ (43,609)	$ (90,419)	$ (157,957)
Denominator:
Weighted-average common shares outstanding, Basic (in shares)	112,706	113,828	113,572	112,907	111,883	111,315	110,875	109,692	113,254	110,948	108,450
Effect of potential dilutive common shares									0	0	0
Denominator:
Weighted-average common shares outstanding, Diluted (in shares)	112,706	113,828	113,572	112,907	111,883	111,315	110,875	109,692	113,254	110,948	108,450
Earnings Per Share, Basic									$ (0.39)	$ (0.81)	$ (1.46)
Earnings Per Share, Diluted									$ (0.39)	$ (0.81)	$ (1.46)