Significant Accounting Policies - Earnings per share (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Significant Accounting Policies
Net income (loss) available for stockholders:	$ 7,217	$ (212,192)	$ (87,111)
Less: Adjustments for losses attributable to participating securities	(89)		(334)
Net income (loss) used in calculating earnings per share	$ 7,128	$ (212,192)	$ (87,445)
Weighted average shares outstanding (including participating securities)	215,646	215,063	214,730
Adjustment for participating securities	(2,656)	(2,571)	(2,509)
Shares used in calculating basic and diluted earnings per share	212,990	212,492	212,221