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								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income from continuing operations									$ 139,371	$ 128,029	$ 121,473
Net income from discontinued operations									0	0	1,687
Net income	$ 31,821	$ 47,565	$ 38,822	$ 21,163	$ 29,203	$ 41,419	$ 35,813	$ 21,594	139,371	128,029	123,160
Income allocated to participating securities, basic									(975)	(889)	(1,075)
Income allocated to participating securities, diluted									(972)	(884)	(1,069)
Net income available to common shareholders, basic									$ 138,396	$ 127,140	$ 122,085
Weighted average common shares outstanding -- basic (in shares)									55,872	56,814	57,730
Basic earnings per share, Continuing operations (in dollars per share)	$ 0.57	$ 0.85	$ 0.69	$ 0.38	$ 0.52	$ 0.72	$ 0.62	$ 0.38	$ 2.48	$ 2.24	$ 2.08
Basic earnings per share, Discontinued operations (in dollars per share)									0.00	0.00	0.03
Basic earnings per share (in dollars per share)				0.38					$ 2.48	$ 2.24	$ 2.11
Net income available to common shareholders, diluted									$ 138,399	$ 127,145	$ 122,091
Diluted effect of stock options and PVRSUs (in shares)									283	459	526
Weighted average commons shares outstanding -- diluted (in shares)									56,155	57,273	58,256
Diluted earnings per share, Continuing operations (in dollars per share)	$ 0.56	$ 0.84	$ 0.68	0.37	$ 0.51	$ 0.72	$ 0.62	$ 0.37	$ 2.46	$ 2.22	$ 2.07
Diluted earnings per share, Discontinued operations (in dollars per share)									0.00	0.00	0.03
Diluted earnings per share (in dollars per share)				$ 0.37					$ 2.46	$ 2.22	$ 2.10