Earnings Per Share - Computation of Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share Basic And Diluted [Abstract]
Net income from continuing operations	$ 17,504	$ 18,259	$ 53,170	$ 53,093
(Loss) from discontinued operations		(46)		(210)
Net income	$ 17,504	$ 18,213	$ 53,170	$ 52,883
Weighted average common shares outstanding	36,856	36,919	36,997	36,854
Income from continuing operations	$ 0.47	$ 0.49	$ 1.44	$ 1.44
(Loss) from discontinued operations				$ (0.01)
Basic earnings per share	$ 0.47	$ 0.49	$ 1.44	$ 1.43
Weighted average common shares outstanding	36,856	36,919	36,997	36,854
Dilutive effect of stock options and restricted stock	949	1,046	950	966
Diluted weighted average shares outstanding	37,805	37,965	37,947	37,820
Income from continuing operations	$ 0.46	$ 0.48	$ 1.40	$ 1.41
(Loss) from discontinued operations				$ (0.01)
Diluted earnings per share	$ 0.46	$ 0.48	$ 1.40	$ 1.40