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, 2016	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net income	$ 47,565	$ 21,163	$ 41,419	$ 107,550	$ 98,826
Income allocated to participating securities	(342)		(278)	(749)	(695)
Net income available to common shareholders	$ 47,223		$ 41,141	$ 106,801	$ 98,131
Denominator:
Weighted average common shares outstanding – basic (in shares)	55,630		56,843	55,904	57,019
Basic earnings per share (in dollars per share)	$ 0.85	$ 0.38	$ 0.72	$ 1.91	$ 1.72
Numerator:
Income allocated to participating securities	$ (341)		$ (277)	$ (746)	$ (691)
Net income available to common shareholders	$ 47,224		$ 41,142	$ 106,804	$ 98,135
Denominator:
Weighted average common shares outstanding – basic (in shares)	55,630		56,843	55,904	57,019
Diluted effect of stock options and PVRSUs (in shares)	281		378	296	479
Weighted average common shares outstanding – diluted (in shares)	55,911		57,221	56,200	57,498
Diluted earnings per share (in dollars per share)	$ 0.84	$ 0.37	$ 0.72	$ 1.90	$ 1.71