Additional Information Regarding Vested and Unvested Options Outstanding (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013		Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, vested	980,789
Options outstanding, unvested	549,276		635,706
Options outstanding, weighted average exercise price	$ 6.84		$ 6.90	$ 6.74	$ 7.35
Options outstanding, weighted average remaining contractual life (years)	6 years 3 months 29 days
Options exercisable, shares	980,789	[1]		828,899
Options exercisable, weighted average exercise price	$ 7.52	[1]		$ 8.55
$2.97 - $5.99
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option outstanding, exercise price, lower limit	$ 2.97
Option outstanding, exercise price, upper limit	$ 5.99
Options outstanding, vested	569,246
Options outstanding, unvested	233,876
Options outstanding, weighted average exercise price	$ 4.06
Options outstanding, weighted average remaining contractual life (years)	7 years 8 months 9 days
Options exercisable, shares	569,246	[1]
Options exercisable, weighted average exercise price	$ 3.90	[1]
$6.00 - $9.99
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option outstanding, exercise price, lower limit	$ 6.00
Option outstanding, exercise price, upper limit	$ 9.99
Options outstanding, vested	11,100
Options outstanding, unvested	315,400
Options outstanding, weighted average exercise price	$ 6.53
Options outstanding, weighted average remaining contractual life (years)	9 years 4 months 6 days
Options exercisable, shares	11,100	[1]
Options exercisable, weighted average exercise price	$ 7.19	[1]
$10.00 - $12.99
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option outstanding, exercise price, lower limit	$ 10.00
Option outstanding, exercise price, upper limit	$ 12.99
Options outstanding, vested	265,100
Options outstanding, weighted average exercise price	$ 11.21
Options outstanding, weighted average remaining contractual life (years)	7 months 17 days
Options exercisable, shares	265,100	[1]
Options exercisable, weighted average exercise price	$ 11.21	[1]
$13.00 - $17.99
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option outstanding, exercise price, lower limit	$ 13.00
Option outstanding, exercise price, upper limit	$ 17.99
Options outstanding, vested	115,843
Options outstanding, weighted average exercise price	$ 15.12
Options outstanding, weighted average remaining contractual life (years)	2 years 1 month 17 days
Options exercisable, shares	115,843	[1]
Options exercisable, weighted average exercise price	$ 15.21	[1]
$18.00 - $18.84
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option outstanding, exercise price, lower limit	$ 18.00
Option outstanding, exercise price, upper limit	$ 18.84
Options outstanding, vested	19,500
Options outstanding, weighted average exercise price	$ 18.06
Options outstanding, weighted average remaining contractual life (years)	2 years 7 months 2 days
Options exercisable, shares	19,500	[1]
Options exercisable, weighted average exercise price	$ 18.06	[1]

[1] The weighted average remaining contractual life of the options that were exercisable as of June 30, 2013 was 4.82 years.