Stock-Based Compensation - Schedule of Information Regarding Stock Options Outstanding (Detail) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, Number of Shares	3,225,204	3,155,631	3,267,838
Options vested and expected to vest using estimated forfeiture rates, Number of Shares	2,953,946	3,019,979
Options exercisable, Number of Shares	1,692,770	2,329,987
Options outstanding, Weighted Average Exercise Price	$ 7.74	$ 6.65
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Exercise Price	$ 7.56	$ 6.67
Options exercisable, Weighted Average Exercise Price	$ 6.70	$ 6.91
Options outstanding, Weighted Average Remaining Contractual Life (years)	5 years 8 months 12 days	5 years 2 months 27 days
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Remaining Contractual Life (years)	5 years 7 months 21 days	5 years 2 months 1 day
Options exercisable, Weighted Average Remaining Contractual Life (years)	5 years 1 month 17 days	4 years 8 months 9 days
Options outstanding, Aggregate Intrinsic Value	$ 18.2	$ 3.5
Options vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	17.2	3.4
Options exercisable, Aggregate Intrinsic Value	$ 11.4	$ 2.5