Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income (loss) available to common shareholders	$ 19,446	$ 2,657	$ 17,539	$ (143,009)
Weighted average common shares outstanding - Basic (in shares)	39,389	39,243	39,523	39,095
Dilutive effect of stock-based awards (in shares)	297	546	352	0
Weighted average common shares outstanding - Diluted (in shares)	39,686	39,789	39,875	39,095
Earnings (loss) per common share - Basic (in dollars per share)	$ 0.49	$ 0.07	$ 0.44	$ (3.66)
Earnings (loss) per common share - Diluted (in dollars per share)	$ 0.49	$ 0.07	$ 0.44	$ (3.66)