Stock-Based Compensation Plans - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 11,618	$ 8,869	$ 8,169
Employees [Member] | Restricted Stock and Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	10,792	8,193	7,269
Employees [Member] | Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	826	676	900
Non-Employee Directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	12,519	9,769	8,879
Non-Employee Directors [Member] | Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 901	$ 900	$ 710