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						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income	$ 14,500	$ (2,441)	$ 55,463	$ 76,239	$ 74,389	$ 30,081	$ 67,522	$ 180,709
Income allocated to participating securities	(78)			(463)			(378)	(1,104)
Net income available to common shareholders	$ 14,422			$ 75,776			$ 67,144	$ 179,605
Denominator:
Weighted average common shares outstanding – basic (in shares)	55,106			55,366			55,167	55,346
Basic earnings per share (in dollars per share)	$ 0.26			$ 1.37			$ 1.22	$ 3.25
Numerator:
Income allocated to participating securities	$ (78)			$ (461)			$ (377)	$ (1,100)
Net income available to common shareholders	$ 14,422			$ 75,778			$ 67,145	$ 179,609
Denominator:
Weighted average common shares outstanding – basic (in shares)	55,106			55,366			55,167	55,346
Diluted effect of stock options and PVRSUs (in shares)	304			260			273	269
Weighted average common shares outstanding – diluted (in shares)	55,410			55,626			55,440	55,615
Diluted earnings per share (in dollars per share)	$ 0.26			$ 1.36			$ 1.21	$ 3.23