Earnings Per Share - Computation Of Basic And Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income	$ (2,441)	$ 55,463	$ 74,389	$ 30,081	$ 53,022	$ 104,470
Loss (income) allocated to participating securities	14		(468)		(301)	(640)
Net (loss) income available to common shareholders	$ (2,427)		$ 73,921		$ 52,721	$ 103,830
Denominator:
Weighted average common shares outstanding – basic (in shares)	55,054		55,323		55,199	55,335
Basic earnings per share (in dollars per share)	$ (0.04)		$ 1.34		$ 0.96	$ 1.88
Numerator:
Loss (income) allocated to participating securities	$ 14		$ (466)		$ (300)	$ (638)
Net (loss) income available to common shareholders	$ (2,427)		$ 73,923		$ 52,722	$ 103,832
Denominator:
Weighted average common shares outstanding – basic (in shares)	55,054		55,323		55,199	55,335
Diluted effect of stock options and PVRSUs (in shares)	0		237		258	273
Weighted average common shares outstanding – diluted (in shares)	55,054		55,560		55,457	55,608
Diluted earnings per share (in dollars per share)	$ (0.04)		$ 1.33		$ 0.95	$ 1.87