Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
	Apr. 30, 2013	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Income from continuing operations										$ 38,129	$ 38,523	$ 64,298
Loss from discontinued operations, net of provision for income taxes												(3,808)
Loss on sale of discontinued operations, net of provision for income taxes	$ 4,800											(4,837)
Net income		$ 8,680	$ 8,267	$ 10,000	$ 11,182	$ 10,106	$ 9,776	$ 9,448	$ 9,193	$ 38,129	$ 38,523	$ 55,653
Weighted average common shares outstanding		33,843	33,620	33,568	33,496	33,316	33,115	32,832	32,273	33,633,000	32,887,000	32,306,000
Stock options and performance stock units										437,000	497,000	251,000
Denominator for diluted earnings per share		34,213	34,138	34,033	33,970	33,785	33,343	33,369	32,616	34,070,000	33,384,000	32,557,000
Earnings per share- continuing operations:
Basic										$ 1.13	$ 1.17	$ 1.99
Diluted										1.12	1.15	1.97
Loss per share - discontinued operations:
Basic												(0.27)
Diluted												(0.27)
Earnings per share - net income:
Basic		$ 0.26	$ 0.25	$ 0.30	$ 0.33	$ 0.30	$ 0.30	$ 0.29	$ 0.28	1.13	1.17	1.72
Diluted		$ 0.25	$ 0.24	$ 0.29	$ 0.33	$ 0.30	$ 0.29	$ 0.28	$ 0.28	$ 1.12	$ 1.15	$ 1.71