Stock Plans - Schedule of Stock Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Restricted stock	$ 4,691	$ 3,456	$ 3,035
Stock options	380	2,459	2,454
Performance stock	6,687	3,296	2,110
Total compensation expense before income taxes	11,758	9,211	7,599
Income tax benefit	4,440	3,375	2,896
Total compensation expense, net of income tax benefit	$ 7,318	$ 5,836	$ 4,703