Stock Compensation Plans - Stock-Based Compensation Expense Included in Consolidated Statement of Income and Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 27,002	$ 27,778	$ 23,010
Less tax benefit	(8,018)	(8,456)	(7,228)
Total stock-based compensation, net of tax	18,984	19,322	15,782
Equity-based awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	22,648	23,736	19,716
Liability-based awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 4,354	$ 4,042	$ 3,294