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, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator:
Net income	$ 38,822	$ 21,163	$ 35,813	$ 59,985	$ 57,407
Income allocated to participating securities	(272)		(243)	(411)	(413)
Net income available to common shareholders	$ 38,550		$ 35,570	$ 59,574	$ 56,994
Denominator:
Weighted average common shares outstanding – basic	56,060		57,212	56,043	57,108
Basic earnings per share (in dollars per share)	$ 0.69	$ 0.38	$ 0.62	$ 1.06	$ 1.00
Numerator:
Income allocated to participating securities	$ (271)		$ (241)	$ (410)	$ (411)
Net income available to common shareholders	$ 38,551		$ 35,572	$ 59,575	$ 56,996
Denominator:
Weighted average common shares outstanding – basic	56,060		57,212	56,043	57,108
Diluted effect of stock options and PVRSUs	296		476	304	525
Weighted average common shares outstanding – diluted	56,356		57,688	56,347	57,633
Diluted earnings per share (in dollars per share)	$ 0.68	$ 0.37	$ 0.62	$ 1.06	$ 0.99