Stock Based Compensation - Summary of Options Outstanding (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding, Number Outstanding	564,783	581,888	587,342
Weighted- Average Remaining Contractual Life (Years)	5 years 10 months 24 days
Options Outstanding, Aggregate intrinsic value	$ 773,157
Weighted-average exercise prices	$ 4.29	$ 4.62	$ 4.68
Options Exercisable, Number Exercisable	456,473
Options Exercisable, Aggregate intrinsic value	586,638
Options Exercisable, Weighted- Average Exercise Price	$ 4.76
Range One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, lower limit	$ 1.90
Range of Exercise Prices, upper limit	$ 2.51
Options Outstanding, Number Outstanding	470,100
Weighted- Average Remaining Contractual Life (Years)	6 years 7 months 6 days
Options Outstanding, Aggregate intrinsic value
Weighted-average exercise prices	$ 2.39
Options Exercisable, Number Exercisable	361,790
Options Exercisable, Aggregate intrinsic value
Options Exercisable, Weighted- Average Exercise Price	$ 2.41
Range Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, upper limit	$ 8.92
Options Outstanding, Number Outstanding	18,877
Weighted- Average Remaining Contractual Life (Years)	4 years 3 months 18 days
Options Outstanding, Aggregate intrinsic value
Weighted-average exercise prices	$ 8.92
Options Exercisable, Number Exercisable	18,877
Options Exercisable, Aggregate intrinsic value
Options Exercisable, Weighted- Average Exercise Price	$ 8.92
Range Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, lower limit	$ 11.36
Range of Exercise Prices, upper limit	$ 12.35
Options Outstanding, Number Outstanding	43,473
Weighted- Average Remaining Contractual Life (Years)	2 years 7 months 6 days
Options Outstanding, Aggregate intrinsic value
Weighted-average exercise prices	$ 13.69
Options Exercisable, Number Exercisable	43,473
Options Exercisable, Aggregate intrinsic value
Options Exercisable, Weighted- Average Exercise Price	$ 13.69
Range Four [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, lower limit	$ 16.51
Range of Exercise Prices, upper limit	$ 17.17
Options Outstanding, Number Outstanding	32,333
Weighted- Average Remaining Contractual Life (Years)	1 year 2 months 12 days
Options Outstanding, Aggregate intrinsic value
Weighted-average exercise prices	$ 16.60
Options Exercisable, Number Exercisable	32,333
Options Exercisable, Aggregate intrinsic value
Options Exercisable, Weighted- Average Exercise Price	$ 16.60