Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Loss Contingencies [Line Items]
Rental expense	$ 2.0	$ 1.3
Future lease obligations under sublease arrangements	0.8
Settlement days of bond transaction	Within one to three trading days
Collateral deposit	0.9
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Contingent obligation for standby letter of credit issued to Landlord	$ 1.4