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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Line Items]
Net income from continuing operations	$ 18,191	$ 19,289	$ 35,666	$ 34,834
Income (loss) from discontinued operations		54		(165)
Net income	$ 18,191	$ 19,343	$ 35,666	$ 34,669
Weighted average common shares outstanding	37,015	36,868	37,068	36,821
Income from continuing operations	$ 0.49	$ 0.52	$ 0.96	$ 0.94
Income (loss) from discontinued operations
Basic earnings per share	$ 0.49	$ 0.52	$ 0.96	$ 0.94
Weighted average common shares outstanding	37,015	36,868	37,068	36,821
Dilutive effect of stock options and restricted stock	927	951	951	925
Diluted weighted average shares outstanding	37,942	37,819	38,019	37,746
Income from continuing operations	$ 0.48	$ 0.51	$ 0.94	$ 0.92
Income (loss) from discontinued operations
Diluted earnings per share	$ 0.48	$ 0.51	$ 0.94	$ 0.92