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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income from continuing operations	$ 18,259	$ 13,708	$ 53,093	$ 40,857
Net (loss) from discontinued operations	(46)	(226)	(210)	(1,253)
Net income	18,213	13,482	52,883	39,604
Basic weighted average shares outstanding	36,919	36,500	36,854	36,521
Income from continuing operations	$ 0.49	$ 0.38	$ 1.44	$ 1.12
(Loss) from discontinued operations		$ (0.01)	$ (0.01)	$ (0.04)
Basic earnings per share	$ 0.49	$ 0.37	$ 1.43	$ 1.08
Dilutive effect of stock options and restricted stock	1,046	1,041	966	1,371
Diluted weighted average shares outstanding	37,965	37,541	37,820	37,892
Income from continuing operations	$ 0.48	$ 0.37	$ 1.41	$ 1.08
(Loss) from discontinued operations		$ (0.01)	$ (0.01)	$ (0.03)
Diluted earnings per share	$ 0.48	$ 0.36	$ 1.40	$ 1.05
Common Stock Voting [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income
Basic weighted average shares outstanding	36,919	36,500	36,854	35,968
Common Stock Non-voting [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic weighted average shares outstanding				553