Earnings Per Share - Computation Of Basic And Diluted EPS (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basic:
Net income (loss)	$ 30,052	$ (81,445)	$ (376,980)
Less: Undistributed earnings allocated to participating securities	(356)	0	0
Undistributed earnings (loss) allocated to common shares	$ 29,696	$ (81,445)	$ (376,980)
Weighted average number of shares outstanding - basic (in shares)	145,295	111,612	105,416
Effect of dilutive securities:
Undistributed earnings (loss) allocated to common shares	$ 29,696	$ (81,445)	$ (376,980)
Share-based awards other than participating securities	$ 0	$ 0	$ 0
Share-based awards other than participating securities (in shares)	5	0	0
Undistributed earnings reallocated to participating securities	$ 0	$ 0	$ 0
Net income (loss)	$ 29,696	$ (81,445)	$ (376,980)
Weighted average number of shares outstanding, diluted	145,300	111,612	105,416