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, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net income	$ 74,389	$ 30,081	$ 79,839	$ 25,086	$ 104,470	$ 104,925
Income allocated to participating securities	(468)		(462)		(640)	(627)
Net income available to common shareholders	$ 73,921		$ 79,377		$ 103,830	$ 104,298
Denominator:
Weighted average common shares outstanding – basic (in shares)	55,323		56,364		55,335	56,414
Basic earnings per share (in dollars per share)	$ 1.34		$ 1.41		$ 1.88	$ 1.85
Numerator:
Income allocated to participating securities	$ (466)		$ (459)		$ (638)	$ (623)
Net income available to common shareholders	$ 73,923		$ 79,380		$ 103,832	$ 104,302
Denominator:
Weighted average common shares outstanding – basic (in shares)	55,323		56,364		55,335	56,414
Diluted effect of stock options and PVRSUs (in shares)	237		468		273	557
Weighted average common shares outstanding – diluted (in shares)	55,560		56,832		55,608	56,971
Diluted earnings per share (in dollars per share)	$ 1.33		$ 1.40		$ 1.87	$ 1.83