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
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income	$ 25,086	$ 24,269
Income allocated to participating securities	(155)	(174)
Net income available to common shareholders	$ 24,931	$ 24,095
Denominator:
Weighted average common shares outstanding – basic (in shares)	56,464	55,941
Basic earnings per share (in dollars per share)	$ 0.44	$ 0.43
Numerator:
Income allocated to participating securities	$ (154)	$ (174)
Net income available to common shareholders	$ 24,932	$ 24,095
Denominator:
Weighted average common shares outstanding – basic (in shares)	56,464	55,941
Diluted effect of stock options and PVRSUs (in shares)	647	345
Weighted average common shares outstanding – diluted (in shares)	57,111	56,286
Diluted earnings per share (in dollars per share)	$ 0.44	$ 0.43