Earnings Per Share (Summary Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net loss attributable to common stockholders - basic and diluted									$ (5,294)	$ (31,738)	$ (98,007)
Weighted average common shares outstanding - diluted (shares)									72,255	73,371	75,604
Basic (in dollars per share)	$ (0.41)	$ (0.03)	$ 0.21	$ 0.08	$ (0.60)	$ (0.07)	$ 0.13	$ 0.07	$ (0.07)	$ (0.43)	$ (1.30)
Diluted (in dollars per share)	$ (0.41)	$ (0.03)	$ 0.20	$ 0.08	$ (0.60)	$ (0.07)	$ 0.13	$ 0.07	$ (0.07)	$ (0.43)	$ (1.30)