Stock-Based Compensation - Employee Withholding Taxes on Stock Awards - Additional Information (Detail) (Employee Withholding Taxes on Stock Awards [Member], USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Employee Withholding Taxes on Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payment of withholding taxes related to stock awards	$ 1.0	$ 1.0