Earnings Per Share - Computation Of Basic And Diluted EPS (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic:
Net income (loss)	$ (13,747)	$ 27,121	$ 17,784	$ (2,560)	$ 50,580	$ 2,290	$ (6,403)	$ (16,415)	$ 28,598	$ 30,052	$ (81,445)
Less: Undistributed earnings allocated to participating securities									(273)	(356)	0
Undistributed earnings (loss) allocated to common shares									$ 28,325	$ 29,696	$ (81,445)
Weighted average number of shares outstanding - basic (in shares)									146,702	145,295	111,612
Effect of dilutive securities:
Undistributed earnings (loss) allocated to common shares									$ 28,325	$ 29,696	$ (81,445)
Share-based awards other than participating securities									$ 0	$ 0	$ 0
Share-based awards other than participating securities (in shares)									128	5	0
Undistributed earnings reallocated to participating securities									$ 1	$ 0	$ 0
Net income (loss)									$ 28,326	$ 29,696	$ (81,445)
Weighted average number of shares outstanding, diluted									146,830	145,300	111,612