Commitments and Contingencies - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	Aug. 29, 2013 sqft	Sep. 30, 2013	Sep. 30, 2012
Loss Contingencies [Line Items]
Rental expense		$ 3,000,000	$ 1,500,000
Company executed lease	16,000
Aggregate leases payments	14,100,000	29,071,000
lease expires date	2027-01
Future lease obligations under sublease arrangements		800,000
Settlement days of bond transaction		Within one to three trading days
Collateral deposit		900,000
Revenues from riskless principal trading		4,500,000
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Contingent obligation for standby letter of credit issued to Landlord		$ 1,400,000