Stock-Based Compensation - Schedule of Information Regarding Restricted Stock Units Outstanding (Detail) (Restricted Stock Units [Member], USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs outstanding, Number of Shares	727,973	708,651	407,765
RSUs vested and expected to vest using estimated forfeiture rates, Number of Shares	595,309	588,170
RSUs outstanding, Weighted Average Remaining Contractual Life (years)	1 year 4 months 6 days	1 year 1 month 2 days
RSUs vested and expected to vest using estimated forfeiture rates, Weighted Average Remaining Contractual Life (years)	1 year 3 months 22 days	1 year 18 days
RSUs outstanding, Aggregate Intrinsic Value	$ 9.6	$ 4.9
RSUs vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	7.9	4.0
RSUs outstanding, Fair Value	$ 9.6	$ 4.9