Stockholders' Equity - Scheduled Vesting for Outstanding Restricted Stock Units (Detail) (Restricted Stock Units) In Millions, unless otherwise specified	Sep. 30, 2013
Restricted Stock Units
Schedule of Vesting [Line Items]
Three Months Ended December 31, 2013	1.5
Year Ended December 31, 2014	5.4
Year Ended December 31, 2015	5.6
Year Ended December 31, 2016	2.9
Year Ended December 31, 2017	1.2
Thereafter	0.3
Total	16.9