Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 M Y sqft	Mar. 31, 2012	Jan. 23, 2012 sqft
Commitments and Contingencies Disclosure [Line Items]
Office space under lease, square feet	53,000		48,000
New lease term, months	123
Number of lease renewal options	2
Number of years lease agreement, renewal option	5
Aggregate minimum lease commitment	$ 15.2
Letter of credit to secure obligations under lease	1.6
Proceed from security deposit related to property	0.7
Rent expense charged to operations	$ 0.9	$ 0.7