401(k) Savings Plan - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Contribution by employer to 401 (k) Savings Plan	$ 664	$ 550
Employee's contributions up to 3% [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent	100.00%	100.00%
Employee's contributions between 3% and 5% [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent	50.00%	50.00%
100% of Matching contribution [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of the employee's compensation	3.00%	3.00%
50% of Matching contribution [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of the employee's compensation	5.00%	5.00%
50% of Matching contribution [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of the employee's compensation	3.00%	3.00%