Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Share Capital	Additional Paid in Capital	Deficit
Increase (Decrease) in Stockholders' Equity
Cumulative adjustment for accounting changes related to leases and tax reorganizations (Note 2)				$ 124,476
Balance, beginning of year at Dec. 31, 2016		$ 10,303	$ 1,342,656	(493,972)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (Note 7)			0
Stock-based compensation (Note 7)			2,496
Repurchase of Common Stock (Note 7)		(8)	(17,908)
Net income (loss)	$ (31,708)			(31,708)
Balance, end of year at Dec. 31, 2017	936,335	10,295	1,327,244	(401,204)
Increase (Decrease) in Stockholders' Equity
Cumulative adjustment for accounting changes related to leases and tax reorganizations (Note 2)				0
Exercise of stock options (Note 7)			1,429
Stock-based compensation (Note 7)			2,112
Repurchase of Common Stock (Note 7)		(5)	(12,737)
Net income (loss)	102,616			102,616
Balance, end of year at Dec. 31, 2018	1,029,750	10,290	1,318,048	(298,588)
Increase (Decrease) in Stockholders' Equity
Cumulative adjustment for accounting changes related to leases and tax reorganizations (Note 2)				(389)
Exercise of stock options (Note 7)			0
Stock-based compensation (Note 7)			2,120
Repurchase of Common Stock (Note 7)		(20)	(37,541)
Net income (loss)	38,690			38,690
Balance, end of year at Dec. 31, 2019	$ 1,032,610	$ 10,270	$ 1,282,627	$ (260,287)